AC vibration

[AmeriLite21]

A couple of weeks ago I was dewinterizing our AmeriLite 21. When I turned on the AC it vibrated really badly. I removed the shroud on the roof and could not find anything on the fans- no wasp or muddabber nests, bent blades, etc. Someone with the same problem suggested tightening the mounting bolts from the underside of the AC. I tried that, and no change. Anyone else have the same problem or know what else to check? Any suggestions will be gladly appreciated.

[EarlJunior]

Have you tried cleaning the fan blades? Also check the area immediately surrounding the fan blades as there may be small bits of crap the fan blades hit as they spin . . .

[RayChez1]

Check to see if the fan is not lose. That is the only thing that would cause the a/c to vibrate. Only other thing that turns is the motor, but I would hate to say this, but if the bearings are going bad it would also cause a vibration. But it sounds to me like a lose fan.
good luck!