vibrating

My Element is shaking a lot while stopped in reverse or drive, or while driving at idle speeds in reverse. This happens regardless of how long the car has been running (or not running), and goes away once it starts moving. The transmission shifts beautifully, and doesn't grind, or show any other...

I have a 2006 automatic. When I'm cruising usually around 45mph, the front end will start vibrating until I let off the gas. I feel it more in the pedals than the steering wheel. I feel like its nothing to do with wheel bearings or suspension. Anybody have any clue?