Actually, I bet it'* the torque strut mount.
Here'* how you test:
Place the car on flat ground.
Raise the hood.
Have a trusted individual start the car.
Set the parking brake.
Foot on the brake.
Shift to Drive.
DO NOT STAND, WALK OR JOG IN FRONT OF THE CAR!!!
Quickly tap the gas to 50% or so.
Watch how the engine moves, Which side of the rear drops farther?
The both sides should move 1/4" to 3/8".
If it'* the passenger side, You need a new Torque Strut Mount. Two Bolts.
If it'* the drivers' side, You need a new Transmission Mount. 7 or 8 Bolts.
If you can't tell which side does it most, guess Torque Strut, It'* cheaper and easier.