My audio

Hi Jack Clarke,

Have you tried plugging & un-plugging the headsets a couple of times? (up words of 10 to 15 time in a row)

Have you tried a SMU Reset?

Have you tried a PRAM reset?

If your still having the issue, have you considered taking the computer to a Genius Bar, and or Apple Authorized Service Provider?

cheers,

-TT

At the Genius Bar, they will look at your computer for no cost, even if you are no longer under warranty. If there is something physically wrong with your computer that requires a repair, then if you are outside of AppleCare, you have to pay for work to be done. But, to have the Genius look at your computer, try a few things on the software side, try to reset the SMC or NVRAM (or PRAM) - that kind of service will not cost you anything.

Follow the above advice, but to expand on the subject, the red light you are seeing is the optical audio signal. The headphone jack supports both analog and digital outputs for use on both headphones and other stereo equipment respectively. The light should not be visible when there is nothing plugged in as it is only activated when it senses a plug inserted.