I've done a ton of research on disc brake squeel on different forums. It seems to be an ongoing issue with all brands, although the symptoms are not always the same. Some people are getting cold brake squeel while others are getting hot squeel. Unlucky people are getting some sort of noise all the time. People have named contamination or misproper pad alignment as the culpit.
I mounted my new BB7's about a week ago, and right out of the box, they never squeeled. After about 3 rides, I was getting pretty loud noises, only on the front, and only during heavy braking loads, such as slow steep declines. I noticed the rotors and pads had this sticky brake feel to it, which was causing the noise. When I midly grip the brake, that nice quiet grabbing noise was replaced with this sticky loud howling.
So on went the laytex gloves and off came the rotors and pads. I first tried cleaning the rotor and pads with dishwasing detergent, which seemed to help right away. the grabby feeling was back, but after a few stops it squeeled again.
Next I tried denatured alcohol and a light/med sanding block. I lightly sanded both sided of the rotor to remove the shinyness, and gave a light scrubbing to the pads. Cleaned everything with alcohol and went for a test ride. Well it sqealed like crazy right away until they warmed up. I went for a 20 mile run with my gf, and they only squeeled on occasion. Heavy braking under steep conditions still caused some rather loud noises.
Having a strong car background, I had the idea of using anti-squeel compound. For those who don't know, brake squeel is mainly caused by resonating brake pads which send strong vibrations to the rotor. This high temp compound is designed to quel some of this vibration. Since bike pads don't have shims, I lightly coated each backside of the pads, and let it dry. After a few hours, I went for a test ride. To my surprise, this made the biggest difference. The squeel is all but gone. I still get a little bit now and then,but a huge improvement in my book. However, since the compound comes in contact with the brake piston, I'm wondering if bits can somehow fall off and contaminate the pads. The solution would be to use a brake shim which cars often use. This will allow you to you use MORE anti-squeel compound, and form a denser, less vibration-prone disk pad. I'm going to try and cut a pair of shims and glue them to the back of the pads and see if that will help even more.
I'm SHOCKED that brake manufacturers don't include a simple clip-on shim along with some anti-squeel compound with their pads. Just seems like a simple solution that gets rid of the biggest complint with disc brakes. Sure this would increase the thickness of the pad assembly, but that can be EASILY solved with Avid's CPS.
Can anyone think of a reason not to do this?