DON'T be alarmed.. This doesn't apply to your class C, but may apply to older class A MHs that are on the Ford F53 chassis. Someone searching for the topic of screechy squeaky sounds may stumble on this topic..
The sound I had was like two styrofoam cups rubbing together. It was coming from the drivers side near where the dashboard meets the windshield. I chased it for almost a year and close to 10,000 miles, then found it, almost by accident.
The large screws that secure the driver side wall to the frame had fallen out and the outside wall was moving (rubbing) against the frame plate.
If you drive an older Coachman MH on a F53, you may want to look at this, particularly if you notice the drivers wall moving in relation to the dash board.
Additional repair to drivers side wall | 2001 Coachmen Mirada 300QB