hi just started to run my avid juicy 5 brakes in done approx 25 mile and there is a noise comeing from the back brake its like a metal vibrating noise and only seems to happen when goin at certain speeds above slow speed any ideas brake disc doesnt seem to be bent but back wheel seems to be slightly buckeld and the bike is brand new dont know if that is anything to do with it or are all wheels slightly out of line it does seem to wobble when i spin it free from touching anything? thanks