Had a vibration on our 30 ft. Class C. Thought it would be a balance issue but before I could get it checked a rear tire blue. So now I think it was tread seperrating or a bulge in the tire. The tires didn't have so many miles but had some age sitting outside. I would have the balance and the tires checked. Another time, had similar but worse vibration intermittently and it turned out to be the calipers sticking. Eventually the starting smoking and had to rebuilt the brakes. Find the cause immediately as it's a safety issue.