If you use the microphone in flash on a chromebook (latest v32 chrome) the noise levels are very high. To fix this you have to go to settings and any change to the mic level will dramataically reduce that background noise level.
e.g goto http://www.onlinemictest.com/ on a chromebook and see high noise level - right-click flash - settings - adjust mic level - much better!
Seems like a bug.