BleepingComputer.com: Weird Vibration With Sound

Hi guys can anyone figure this for me? every time i receive an email or play an audio file online the sound vibrates or repeats itself for a while before it turns off. I get a 'clunk' type sound to let me know that an email has dropped in the inbox..but now it goes 'clunk clunk clunk clunk' and on for a bit before it goes off. If i play an audio file online when i close the window that sound vibrates too. Any ideas?? the drivers are fine i've checked them i'm on vista home premium and this is a recent problem...thanks guys ROZ