I just had my components moved over to another frame (same model, 2011 vs 2012) and now I have a buzzing rear brake when I apply the brakes between 25%-75%. The noise is loud and seems to originate directly from the contact point. No chattering, no squealing. The wheels, brakes, and pads are the same as on the previous bike...Ultegra brakes, Reynolds blue pads, carbon braking surface. So far I have done the following:

* Realigned the brake pads (set the toe in by maybe a mm)
* Swapped pads front/back then aligned again
* Tightened the allen bolt behind the brake (it was loose)
* Sanded the pads (removed the sheen)
* Wiped down the rims
* Realigned the brake pads
* Removed and reinstalled wheel

Am I overlooking something?