Do you feel it in the shifter when changing gears?
Most likely, you have a drivetrain issue.
You're going to have to inspect it starting at one end or the other.

I'd do as John says and check out the rear drive dampers first.
Check the rear gear oil.Rear tire have any service at all?I doubt clutch trouble at 30k.
I lost my clutch (PLATE B, CLUTCH 22322-MZ0-000 $50.29) plate at around 36K. That was 80K ago. Never had any issue with a pumpkin.