I have a set of Avid Mechanical disc brakes. I've had them for over a year, with no annoying noises. Now, for the past two sets of pads (One kool-stop and the other avid), if I lightly apply brakes, it makes this extremely loud sound, kinda like it's vibrating...I don't really know how to describe it. I tried different pad and barrell adjuster adjustments, but nothing seems to work...If it matters, it only happens on my rear brake. Also, I know this might be a problem with other people, but my disc brakes squeak a LOT, no matter how hard I pull the lever. This also has only started happening in the past 3 months.