I would agree with tightening the arbor nut. Once snugged to remove
the obvious play, test it by hand turning. If that feels good, spin
it with the motor (no blade, of course) a bit. If all is good, spin
it, more, with the motor. Check for heat build-up in the bearing
area, also, just in case something is too tight, but not visably
observable.

I don't suppose there is any mention, anywhere, of the arbor nut
having a specific torque, for its tightening?

Otherwise, give Jet a call.

Sonny