Virus...

Not long ago i received this friendster message from my former classmate (don't know her really well when we were classmates either). I opened the message and at first it looked like another one of those stupid chain messages (oh ya don't ever send those to me i don't believe in those craps and if you really believe in those stuffs i'll forward them back to you 10 times as many so.. have fun finding 10 times more people!). Ok back to the stupid message, so as i was about to delete the message this loud sound suddenly bursted out from my speaker. So thinking that its another prank message i switched off my computer and on again, and the sound was still there. I had no choice but to unplug my speaker. So today, (a few days after i received that message), i tried to switch on my speaker but the sound is still there. The lousy AVG can't detect any virus so i don't know what it is. If anyone has any suggestions as to how to solve this problem please post on my tagboard or sms me Thanks!! I'll hate to have to reformat my comp...