Try one of the Mills .75cc clones - Irvine, or K-Mills, or the Russian one from Carlson. Or if you can find one, the MP Jet .04 Classic, another sideport diesel, is very quiet. Most of the electrics that I've come across, apart from the small ones, are noisier than these diesels. Switching to glow for a moment, the Thunder Tiger GP07 is very quiet as well.