Find the source of the noise. Check the piston slap, the valve-train and motor mounts in the engine of the generator; refer to your manual for specific locations. Also check the exhaust system and compartment box.
Apply 5W-50 to the piston slap if that is where the noise is coming from. If that does not work, try overhauling the engine of the generator.
Set the clearance of the valve-train if that is where the noise is coming from. Also try replacing the lifters on the valve-train.
Replace the motor mounts if a low frequency noise is escaping from them. As the mounts age, they begin to dry out and rot. Replacing them should firm up the way the generator rides so it won't vibrate as much.
Check the exhaust system to see that the pipes extend past the body of the RV. If they don't, this could be causing the noise. The only solution for this problem is to replace the exhaust system.
Apply 3M noise dampening product if the noise is coming from the compartment box. This product is used to dampen the noise from car doors. Spray this product on the compartment box to help reduce the generator noise.
