Hi all, I have noticed a strange vibration recently... any time I accellerate the car seems to vibrate, it is most noticeable from 3500 - 4500 in 4-6th. lettting off the gas makes it go away. you don't have to slow down, just ease off the gas. The car is due for it's 30k checkup so I am hoping the diff fluid change will resolve it. I just bought new rear tires and the problem continued after the tires.

Any thoughts?