I have this problem. It has something to do with the wireless system I have two Mac wireless routers (express in my main office and the other for streaming music in the den) and a wireless-N-Router by Rosewall in the dining room to pick up signal (I have thick plaster walls.) When I unplug the Rosewall or go in the den, the problem goes away. There is some interference issue -- cannot figure it out, but at least it is not a hardware problem (I don't think.) It is rather annoying, however.