Garrard 301 motor and rumble

I had my 301 restored but I still complain about rumble at high volume. Iv'e been bitching about the plinth I made, but I just lifted the platter to see if perhaps the motor was the issue. when you engage the idler and apply a little pressure to engage fully, I feel the vibration. Either the brass speed selection post is not true or its the motor transmitting the vibration, but the motor seems very smooth.

What steps should I employ to figure this out?