when i use the brakes quite hard on my new bike im getting a "cracking" sound coming from the rear brake.
i can also get the same noise if im off the bike and rock it backward and forward with the brake applied??
ive checked everything is tight and nothing was loose??
only happens if i squeeze the brake hard??
brake is a new style shimano xt trail with ice tech rotor.
its fitted to a 2011 pitch and all the bearings/bushes in the rear seem fine too??
any ideas??

