Look at putting some DynaMat Xtreme in the cabinet where the generator is. Don't block off any holes or vents, but cover the entire inside.
I used that stuff on my old Corvette and now I have a 69 big block Corvette that has NO RATTLES, and is quiet inside. The DynaMat Xtreme works like a charm. NOw, I'm pretty sure that somebody will see this and tell you to go to Home Depot ot Lowe's and buy the thin insulation that has bubble wrap between 2 sheets of aluminized coating. Go ahead and get it, then install it. You'll be taking it out and doing something different, be cause it doesn't work. Ask me how I know...