My truck as started making this awful sound. like a chatter,vibration, rattle type noise.
It happens at 800 rpms.
Not every time without fail, but more often than not.
Sounds like it is coming from underneath the truck. I've not been able to really narrow it down.
It almost sounds like a heat shield rattling against something.
Below 800 rpms, nothing, above 800 rpms, nothing.
Doesn't matter if it is in gear or not. Moving or not.

Sometimes it will do it within a few blocks of my house. Other times, it won't make a noise all day, then out of no where, start up again.

It doesn't effect the way the truck runs.
Doesn't feel like the transmission is dragging or not shifting or anything like.
Does it in park, neutral, in gear, sitting still, moving, A/C on, A/C off,

Other than happening at 800 rpms, the only other symptom I can find is that there is a hum/whine that comes from the intake tube when the throttle plate is closed. It isn't really loud. If you weren't listening for it, you probably wouldn't notice it. I almost think that I only notice it because I was paying so close attention because of that rattling noise. The bit that I've been able to research about the hum/whining sound, people have said that it is normal. I don't know, never owned a ford before.

The rattle is engine speed based. You can hear the ratting slow as the rpms fall below 800 and it speeds up as the rpms rise above 800. but by the time you get +/- 100rpm, you don't hear it anymore.

I got under the truck and didn't find any loose heat shields. Nothing appeared bent or anything like that.

I honestly can't think of anything that would be happening at 800 rpms that would cause that.

any Suggestions?

truck is a 2003 F150 with the 4.6 v8 in it. automatic tranny. just over 120K on the clock.
----------------
Videos of the noises.

Link to video of the rattle. chatter noise.
http://www.youtube.com/watch?v=7O4qih5nqP8

and the whine/hum intake noise
http://www.youtube.com/watch?v=ADiFFcBkhIA

 

Check belts, pulleys, AC Compressor, PS pump, water pump and harmonic balancer. Cant remember if the trucks have a clutch fan or electric fan. If mechanical,.. check the fan clutch.

Otherwise if its just a rattle,.. could be just loose exhaust components,.. check the tail pipe/s.

This is why I stress for people to focus on preventative maintenance. To take care of things BEFORE they start making noises and cause problems. I havent been broke down sitting on the side of the road in over 15 yrs,.. (Knock on wood).

Hurst

 

This rattle could be anything, it's a truck. A rock could be stuck in a motor mount or sitting on top of a frame rail, or it could be exhaust heat-shields etc. etc. like Hurst said.


-On a side note

Hahaha, no matter how many times a technician says to do preventative maintenance, people won't. One of the major reasons I got out of the business. So many people think they are being "ripped off". For every one person that does maint there's probably 10 that don't and they think they are saving money because we technicians are out to make a quick buck off of them. It's every good technician's dream to start up an honest shop, but the shops only end up putting the honest technician through hell will ridiculous hours and little compensation. I found it a lot easier to do good work on cars that have been abused, I just buy and resell them no customer to convince service is not useless

 

+1. I would check the heat shields on the exhaust and the cats. Hopefully you don't have a mystery bolt floating around.

 

Belts visually check out.

The only pully in question is the idler/tensioner arm only because I'm not used to them. it does move as the belt turns but "they" say that's normal. I'll be getting a long screwdriver on it later today when I have assistance with the throttle. but, the noise does seem louder than what I would imagine a pulley to make and does sound lower, like under the truck lower.

A/c compressor, from what I can tell, is operating as it should. The clutch kicks on and off. No distinctive grinding coming from it. The noise doesn't change with the a/c and happens regardless of the a/c being on or off.

Power steering pump. Again. From what I can tell is fine. It isn't whining. I can't feel the chatter in the steering wheel, and this kind of sound I would imagine you'd be able to feel it. Turning the wheel while it is making the sound has no effect on the sound.

Water pump isn't weeping. This noise sounds "bigger" than bearings going bad. But I will give it a listen with the screwdriver while I am in there anyway to rule it out.

My first though was that it could be the fan. It seemed like a similar kind of noise. But when I pushed on the fan shroud to make it make the noise it was distinctively different. The fan and shroud are plastic. The noise I'm talking about is much more metallic.
Only way I can really describe it is it sounds a lot like when you make a sheet of metal make that "ggrrrr" sound when you vibrate it just right. It doesn't have a "tick", "ting" or a "cling" type sound to it. My initial thought the first time I heard it was valve chatter. It sounds a lot like valve chatter, but lower in pitch than any valve chatter I've heard before. And it sounds like it is from underneath the truck, which is what made me think it was the transmission but it will make the sound in and out of gear.
I'm not too familar with automatic trannies.
Even though it is in neutrual, does the torque converter still engage? Does/can the torque converter make a chattery rattle sound that matches engine speed?

It doesn't sound like "just a rattle". It has more of a crunching, chattery kind of sound to it. I'm going to attempt to make a recording of it with my phone and see how that turns out. It is definately coming from the front half of the truck. From the front doors forward. When you are standing in frnt of the truck with the hood open, it sounds like the noise is coming fron the rear of the engine bay from down low, but it doesn't seem like it is one distinctive side or the other.

I did try to check the heat shields and such under the truck. I couldn't bump anything loose with my hands. The heat shields weren't touching anything. Hopefully I can narrow it down further when I get some help over here.

Is there anything that happens at 800 rpms?
Like is there an air/smog pump like the older trucks that engages then?
Or does the torque converter begin to lock up then?
Egr valve opens?
Variable valve timing solenoids? (Fairly certain the 4.6 triton does that, or am I getting engines mixed up?)


I hear ya with the preventitive maintenance. I'm trying to get on top of all of those things with this truck. I've not had it for very long and at this point I'm assuming that not much has been done with it. Previous owner (other than the dealer) was an older lady (no offense) which I found out listening to the recordings on the little digital recorder on the visor.

 

Here's the best I can do as far as recording the noise goes. At least until I can get some help over here.

http://www.youtube.com/watch?v=7O4qih5nqP8

and this is the noise coming through the air intake. I'll rev it up some, and as the RPMs fall, it makes that whining, hum noise.

http://www.youtube.com/watch?v=ADiFFcBkhIA

 

This is very true. 95% of the new people who post on tech forums only do so because they have a problem. They only want to pay for things that are causing immediate issues. If they can get another 5000 miles out of those ball joints before the wheel falls off then they will ride it out.

Most advise we give here (At least this is my opinion) falls on deaf ears.
Example,..
Vehicle wont crank.
Head lights work, horn makes noise.
Never tried jump starting it. Never put an amp test to the battery.
No idea how old it is. Came with the car.
So from advise they get from people that dont know the car say to go out and buy a new battery.
They buy the cheapest battery on sale turning in a battery that was barely a yr old and had more CCA.
Car still wont start. Turns out it was the starter.
Now they have to buy a starter and have a cheaper battery that goes out 2 yrs later when the one they had probably would have lasted another 3 - 4 yrs.
Doh.

This goes on everyday somewhere. People fail to realize that maintaining a vehicle over the years will cost as much as owning it did in the first place. When buying a used vehicle 90% of the time you are buying someone elses problems. Very rare to find a used Mustang or Truck that have been meticulously maintained despite what the owner claims. "Meticulously Maintained" seems to be a matter of perception these days LOL.

Hurst

 

One thing to understand about the 4.6,.. a 4.6 is a 4.6 is a 4.6. No matter what its in,.. Mercury, Ford or Lincoln. Triton, Intech, Mustang, Truck, Crown Vic,.. what ever. They are ALL the same motor. The main difference between the models will be the intake. Each chassis had its own unique intake and induction assembly. But from the heads down,.. they are the same motor.

The are 2 primarily different 4.6 motors. The 2v and the 4v. 2 cams and 4 cams. There are only 2 different versions of the 2v. The NPI and the PI. All original 2v 4.6 motors from 92 - 98 no matter what they were in were NPI (Non PI) motors. Only the Mustangs got PI (Performance Improved) motors in 99. The only difference between the NPI and PI motors are the heads, cams and lower intakes. The upper intakes usually stayed the same. 4.6 trucks did not get PI heads until 01 model year.

Aside from all the confusion describing the difference between the NPI and PI. EVERYTHING between these motors is interchangeable,. visually they all look identical unless you know what to look for.

2003 you should have a 2v 4.6. No variable valve timing. Aside from the intake,.. the block and heads should be identical to whats found in 99 - 04 Mustangs. The newer model 04+ had a 3v 5.4 available. These did have a version of VVT (Variable Valve Timing).

Not sure about the trucks. But in the Mustangs the 4.6 did not have a smog pump. Its a very efficient small motor.

Cant really hear anything distinctive from the first video. What ever was used to record the video couldnt reproduce an accurate audio sample. Sounded like a lot of distortion to me. (No offense).

The second video I could make out a humming noise from the intake duct. Sounded like it has a crack or leak in it somewhere and if so would be very bad. Any kind of intake leak between the MAF and TB would produce a lean condition as the engine is getting more air than what the MAF is reading. The front O2's should detect this and the computer will compensate by turning up the fuel causing the motor to run pig rich. When in fact,.. the air coming in the motor has not changed at all,..only what the MAF is reading has changed.

Not saying this is for certain your problem. I am not there.

Check to make sure the air intake is sealing correctly between the MAF and the TB. Make sure nothing loose floating around inside of it,.. (Lost tools?).

At 120k it would not hurt to pull the air intake assembly off entirely and inspect the TB blade. The whistling/humming noise could be from air by passing a dirty blade that is choked with gummed up debre.

Something else that noise sounds like from past experience. The PCV on these make an awful racket when they go bad. I thought I had a leaking intake once when it turned out the PCV was bad. When replacing it make sure the grommet to the valve cover is still in good condition else replace it with the pcv. Check the vacuum line coming from the intake to the pcv as well and the there should be another 'bypass' vacuum line from the front side of the IAC that goes into the air intake in between the MAF and TB. ALL vacuum lines no matter how miniscule are crucial on 4.6 motors. The sensors and EEC are extremely sensitive to vacuum signals. If even remotely questionable (Dry, hard or gummed up) replace the vacuum lines.

My money is on the PCV. But bare in mind,.. I'm not there. You are.

Hurst