J- I don't know what year or model coach you have (you might want to add that to your iRV2 "signature" so you don't have to repeat that each time you post), but my coach has ACME Radiator & Air Conditioning
parts in the dash. They have a Quick Tips
link on that page which suggests blower vibration can almost always be traced to debris such as paper, cellophane, etc., being sucked up into the blower wheel via the return air door. Occasionally, a blower wheel on the motor shaft may be broken or may have come loose.
I'm not sure if that's the issue w/your unit. If it happened all of a sudden, probably so. If it came on slowly, it might be simple freezing up of motor or blower cage bushings w/ crud over a long period. Fans seem to attract dust & dirt over time w/a sort of static cling until the bearings are overwhelmed. You could remove the blower cover behind the gen slide cap, passenger side, & see if the blower is accessible there to clean it. Also, my unit has a tag w/the following phone number: 800) 552-2263, or you could call the numbers off the website to see if they offer tech support.
IIWM, I'd not use the dash AC till you get this resolved. If it turns out to be a dislocated blower motor shaft, you will be progressively ruining the blower/cage assembly by running it. You can run the gen & roof air till you get it fixed.