yeah, not 100% on the cause, but I have found that lots of cars do exactly what mine has started doing with the whole kicking up to high even thought it isn't really needed.
To me, it seems like the pump starts to die off so it doesn't flow as much as it should at the lower voltage levels, so the fuel controller kicks it up to high to compensate for it. When it does that, it doesn't regulate the voltage so the pump can draw whatever it can/needs to, through the circuit allowing it to maintain the higher flow levels that are needed.
From what I've been able to research, this could quite possibly be the source of a lot of people's "hard to drive in traffic" complaints. A lot of people will bitch that the car just doesn't have enough low end torque to make it an easy drive. The thing doesn't really wake up until you get over 3.5K rpms and at that point, you're out accelerating traffic. Most people just write it off as the car weighing a lot. (3,600 plus pounds) But in its original function, the fuel pump wouldn't kick over to high until about 3.5k rpms anyway. So if the pump just wasn't flowing enough, that would limit the response and power in the lower RPMs. Combine that with everything else that wears out over 20 years and that's more than likely the reason why.
I had a friend who's turbo car made that same noise and he was making 385 to the wheels on his pretty much stock everything motor. With no limit on the voltage the pump could draw, it was able to keep up. He could have made the same power, but probably got a little bit better response and maybe better MPG if the pump was swapped out for a fresh one.

I'm fairly certain that we are going to be ordering parts tonight.
So when I get things in, I'll be doing little write ups about each one. Hopefully it will be able to expose some of the little truths in all of this speculation

I appreciate you asking man.

How's your's treating you?