This is kind of a dumb and simple thing that can make for overly loud engine noise and road noise: Is your doghouse cover properly seated down snug into it's rubber sealing rim ring ... and are the locking clamps that hold the doghouse tight down onto the sealing ring still in good condition, adjusted for maximum tightness, and fully engaged?
We have not yet had this issue with our Ford chassis based Class C, but we had a Dodge van based camper once where this definitely caused a noise problem ... and boy was it loud when even one of it's doghouse motor cover clamps was not properly locked down.
