Dodge Brothers Club

I drove my 24' home last weekend and put about 150 miles on it. Hot or cold it starts right up and never misses a beat. 25-30 MPH is pleasant, 35mph is okay and above that there's something between a buzz and a vibration. Is that the nature of the beast or is that indicative of catastrophic failure?
It feels like engine or drive train vibration. The suspension and steering pins/bushings are all fresh and tight.

That's exactly what i was thinking.
Thanks for the input.

At 35 his tongue is hanging out. Don't push it.

The rear engine support was a little loose in the frame. After tightening that and refreshing the carburetor it's much improved and felt fine at 50MPH, (yikes), on a smooth road. The brakes, wheels, engine and 98 years of age are reasons I don't plan to do that often, if ever.
The instruction book calls 2000 RPM, (45 MPH), "maximum power". 50 MPH would be about 2225 RPM. I thought I had seen 2800 RPM as maximum speed. I don't know where I saw that and can't find that now. Does anyone know what the max. RPM is?