Weird and the speakers I assume were working within a reasonable time prior to this issue and/or using your headphones?
If you have another user account try switching to that user see if it isnt user specific or create a new user to try it out on.
Otherwise shut down; take out the battery, and hold the power button for a few seconds; this resets the SMC.
place the battery back in, boot the machine and immediately hold (COMMAND OPTION P R) that resets the PRAM and might clear up some inconsistencies with it feeding through the ports etc.
see if any of that has an effect...