Windows noise at highway speed

Are you talking about the House Windows? or the Cab windows?

If it is the House windows that are your problem there is an owner on the Buying a Rental Thread that has a Majestic that used This Method

I just did a basic search for your complaint and there are some that have changed out the felt and experienced issues. Some commented that there was silicone in the channel and that cost them a lot of time. Others had success. Depending on your ability to repair things there is felt available you can replace in the channels. Also a call to your local mobile RV guy is always helpful. They come out, do the work and you are on your way.

From the sounds of things, I suspect that the best solution would be renewing the gasket material. It ought to be available from the window manufacturer, likely among other places.

Other than that, it might be practical to wedge the windows in place when traveling with e.g. a couple of toothpicks or a folded index card or something.