I just picked up an '11 tsx (300 miles on it now-originally 60) and I noticed, more so on harder braking, that there is a very slight vibration in a quick pulsating rythem. I don't know if the rotors are warped or if it's an abs thing. I hear no noise or squeeks. It's more noticable on long braking and braking on a downhill slope. Is this normal? or should I have the dealer check it out.