Generator Muffler Mods

I have a typical 5000 watt open frame construction generator that I use at home for emergency power. I fitted an exhaust pipe to it that is routed to the outside of our 2 car garage where the generator is used. With the exhaust going outside, it is unreal how loud the mechanical sound from the generator is inside the garage, as others have mentioned. I don't think a muffler will do that much to reduce the noise. With the generator exhaust going outside, I can now at least mostly close the garage doors so the neighbors don't hear as much noise.