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.