Noisy freakin' brakes!!

Feanor

I have a pair of XT discs on my mountain bike as well, and they rarely squeal or squeak.

Most important thing is that you didn't mention your break-in procedure for the new pads... Did you use them on a continuous downhill run as their first use? If you did, the pads were not contoured to the disks, and the hot spots that developed glazed those locations so that they became very hard compared to the spots that weren't contacting as firmly. This causes squealing and also a grinding sound during braking. disc brakes hate going from cold to blazing hot rapidly when they are still new... Once they are mated to the disc by a proper break-in it spreads the heat load more evenly and helps with dissapation so after they are properly broken-in they don't mind getting hot as much...

Properly set brakes need to be modulated during the break in period of about 20 miles or so. So that the pads are perfectly mated to the discs (a lapping process) During this time you have short periods of hard to moderate braking and then release to let them cool, then repeat. You get this kind of braking with normal use, but if you had a long downhill run before the brakes were mated to the discs then it would cause problems.

Do you find in addition to your loud brakes that your braking force on the fronts is not as powerful as a decent set of v-brakes? If not and you have 60 miles on them then there was a problem braking them in... The XT discs on my mountain bike are so strong that with two fingers on dry pavement I could easily brake hard, compressing the front shocks to their hardstops and then flip over the front bars if I wasn't careful...

Other things to check are rotor warp, loose rotor mounting screws, missing caliper return springs, sticking pistons, and grooved disc surfaces...

Good luck to you!

Feanor