The volume up/down sound effect is no longer making the distinctive popping sound on my 15" 2011 MBP. It doesn't make the sound whatsoever, but when I hook my laptop up to my HDTV via HDMI w/ mini displayport adapter, the popping sound goes off continually over and over. I believe my adapter is broken, so I've ordered a new one, but anyone have an idea why it has stopped making the sound when it's just sitting in my lap, not connected to anything?