Currently Being ModeratedMar 27, 2012 4:25 AM (in response to Thomas Thompson1)
See this thread, one of many, which may or may not be your issue.
Currently Being ModeratedApr 21, 2012 7:05 PM (in response to Thomas Thompson1)
I don't think anyone has found an answer to this. The common thread seems to be the Snow Leopard update. All solutions offered thus far (MIDI controls, PRAM reset, SMC reset, preference reset, blah blah blah have not worked.
It is just plain frustrating that this has not been fixed by Apple.
Currently Being ModeratedFeb 16, 2013 7:02 PM (in response to Thomas Thompson1)
I had same problem. Go to system preferences, then sound, sound effects tab, then select headphones on "play sound effects through (field).
Confirm on the output tab, also set the balance and volume if you wish.