Since the OP has found his problem, I hope you don't mind me posting about mine which is similar, instead of starting a new thread.
I just moved to San Francisco a week ago, and as you might be familiar with, this city has quite a few STEEP hills. I've been driving around a lot the past week getting situated, and it seems to only ever happen on the steep hills, but I've been getting a horrible grinding noise and feeling. On more gradual declines and on flat ground, it doesn't do it and brakes normally. I replaced rotors and pads front and rear and front bearings within the past year, and repacked the front bearings more recently than that. Before my move last weekend, I checked the tightness of the front bearings as well. After first hearing the noise, I was in high-panic mode, so I jacked up all four corners quickly, took off wheels and tires, and did my best to look for a cause to the problem, but couldn't find anything. I also very quickly loosened the passenger side front bearing nut just a smidge because it seemed a little too tight. Mind you, this was in a random parking garage at 10PM with my nervous mother in the car, and her response of "I think it's just the car scraping" was not making me feel any better.
Rotors looked okay, and pads looked okay too, with plenty of material left on them. Because it only happens on the steep hills, my only thought is that the brakes are getting hotter than usual which somehow is causing this grinding. I've never heard this noise before, and never heard of hot brakes causing that noise either, but that's all I've been able to come up with. Any ideas? I just signed a lease on a place today with a garage space, so I should be able to take things apart and look into it further next week or so. Just wanted to get a head start on potential solutions.
