Quite a few people are using 2-stroke oil to quiet their engines
http://www.ft86club.com/forums/showthread.php?t=21980 (among other threads)
I've started using it as well. Ashless (TC-W3) is supposedly better since it's meant to leave no residue. People have had success at ratios as low as 1:1000 (50ml per tank), others are sticking with a 1 oz/5 gal ratio (approx 1:600). I'm still on my first tank at 1:750 (~70 ml/50L) and it's working well. The engine is much quieter overall and crickets show up much less frequently and are quieter when they do.