http://www.alpharubicon.com/altenergy/gensetquiet.htm

When the lights go out here in Virginia, you can hear the generators run for miles away. I looked around for ways to make mine more stealth because I dont want to advertise that I have power at times when times are bad.

I found this to be the best option and you can get a old car muffler from any junk yard for next to nothing.