My 07 Pacifica had a bad front motor mount. I had both the front and back replaced and now I have a weird vibration / louder than normal sound when excelerating under a load. Normal driving, slow driving around town, I don't feel much. I stopped on my driveway, which is quite steep and as I accelerate, there is a definite vibration and humm. I brought it back to the dealer and they feel possibly that one of the mounts installed may be defective. Hummm...I feel as though somthing is out of wack.

 

Ok, so the dealer puts the car back on the rack he finds the newly installed mount, on the rear, is vibrating pretty bad. He replaces it and the vibration is now gone. I am not 100% sure the new mount was defective or they found something installed wrong. Either way, he fixed it.