I'm hearing a high pitched squeaking noise from the left rear whose frequency changes with wheel speed, that will occasionally intensify into a grinding sound, and other times dissappear altogether. Applying the brakes or parking brake does not seem to change the sound. The interesting thing is, the noise does not happen in reverse, and will often times go away if I turn the wheel to the right (with vehicle moving, of course), but intensify when turning the wheel to the left. I have jacked the rear end of the car up, and didn't visually see anything wrong. There is no play at all in either wheel, and the squeaking does not seem to happen if I have the rear end of the car jacked up and spin the wheels by hand. I even pulled the wheels - my rear disc pads look close to new; not so sure about parking brake pads.

I had originally thought it was a wheel bearing, but the sound does not seem to get worse with increasing speed (aside from the increasing frequency of squeak), and there is no play in the wheels nor is there any gear oil leaking. Because the noise disappears in reverse, I'm thinking it's possibly a parking brake shoe. Any ideas?
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85 245 DL - 91 Mazda MX6 Turbo