Sounds like it could be the transaxle mount, but I would consider inspecting the torque strut as well. I have included diagrams and instructions to replace all of the mounts if necessary.
Right Side Removal
Install or Connect
Note: Guide motor mount into location while lowering engine.
Left Front Transaxle Mount
Left Rear Transaxle Mount
Please let me know if there is anything else I can do to assist you.