Pulsing screech in one break
 

2002 P5 33,000 miles
About 3 weeks ago on my way to work a screech sound started comming from my rear driver side wheel. It sounded a bit like a wear indicator warning of a thin pad. I pressed brake pedal a bit, no breaking effort, and the sound stopped only to resume again when I took my foot off the brake pedal. It continued another 10 min. to work. That night there was no noise during my ride home.

But since then it's happened twice more each time after about 5 minutes of travel at 70 mph.

I didn't see anything that might cause the noise when I installed my snow tires & wheels. Brake pads are all about 4 mm thick so I've still got several months of wear left.

Anybody have any ideas what's causing the noise?