I noticed a while ago that I was getting vibrating coming from the front end, but not all the time. I finally figured out what it is. The front rotors are heating up after I drive a while if I am doing alot of hard braking, and the rotors are warping. Once they cool down the problem is gone. Both sides seem to be doing this (there is no pulling to one side). I recently changed to a larger master-vac, which may be exacerbating the problem, but it was doing this before too. Why is this happening? Are the callipers sticking? If so, what is the fix? If not, what else could be causing the rotors to heat up so much?