After reading your response, you could check the following. Speakers should
be checked for the possible culprit. If speakers are OK, then your soundcard
may be at fault. In that your PC is fairly new, it should still be under
warranty
that you could get it repaired or replaced at no cost to you. You could also
try a system restore back a couple of weeks. You'll lose everything you have
added since then. You can go back up to 90 days.
Start>All Programs>Accessories>System Tools>System Restore