Has anyone heard this noise before?
 

I have an 88 911 coupe. I was at the track last week shortly after replacing rotors, pads, e brake linings. I ran my run group and when the checker came out I was on my cool down approaching the pits, so I was crawling , and heard a harmonic noise from the right rear. When I touched the brakes the sound went away, until I released the brake pedal. I checked teh ebrake lining no problem, checked the pads & rotors, no apparent problem. It sounds like an out of round rub. Please HELP!!! Any ideas or thoughts?
I appreciate all thoughts...ideas...concepts

Does the rotor need turning? If it is an out of round rub the rotor could have a slight warp in it.

I had put the bolts on backwards to the dust shield once and the head made contact with the rotor (just the slightest bit) and sounded like the light scrubbing you describe. Evidently the nut and head of the bolt were different thicknesses. When I norticed it and swapped it back everything was fine.

Sounds like a sticking caliper to me. Sometimes you can have this problem just from heating up your brakes - sometimes it just gets worse and worse... Mine did this so ended up rebuilding the calipers.