Weird noise from rear wheel (i think)

[stateofidleness]

I've had quite a bit of maintenance-free miles ('00 base), but recently I've noticed this sound coming from the rear driver's side wheel (i think). I say sound because I can't really describe it very well. It's a "squeaking" type of sound, almost a chirp.. kinda like turning the wheel while standing still on concrete pavement.

Sound and intensity change with speed (definitely sounds "rotational"). I can really only hear it when going really slowly (braking to a light, taking off slowly, etc.). Any faster and engine noise drowns it out. I can hear it "reflecting" off the median on the highway and buildings though when at speed.

So it's gotten to the point of being "embarrassing" because it's loud enough that people can hear it in parking lots, stop lightss etc.

Tonight, I took the rear wheel off and visually inspected it. Nothing out of the ordinary, and no odd wear pattern(s). Visually inspected the rotor, caliper, brakes, etc. Nothing odd there either.

It's VERY hard to pinpoint where the noise is coming from because it only does it when the car is moving and I have no way to stick my ear out there to isolate it. I have no clue what it is and it's kinda got me stumped...

I've also tried "bouncing" the rear end of the car on both sides to see if it was suspension-related, but no noise came from doing this and I don't hear any change in the sound when I go over bumps or speedbumps, etc. No leaks or fluids on ground either. No recent maintenance or replaced items.

Anyone else experience this or have an idea of what to check?