I've noticed a moderate vibration in my car around 30 to 40 mph. It does not feel like a tire balance issue as I don't feel it in the steering wheel and it goes away if I release the accelerator. It lasts at most a couple seconds, and it is hard to tell if it is related to the shift points at all. I tried running the car at 2000-3000 rpm in park and did not feel any vibrations. The car shifts fine, but I'm starting to think it is transmission related. Any ideas? Thanks.