Mine does the EXACT same thing...not present at startup, will start a low buzz, static sounds after a few minutes (it seems to me that the static is coming from near the right speaker/ floppy drive area); and lately I've noticed will go away after 20 minutes or so. I have not been able to find a solution, and it's not very loud, it's a very low static sound. When I have time, I plan on a full cleaning of the sub/woofer power supply.