First things to tryEdit
Always check your connections. Make sure you've got the right cables plugged into the right ports and that the plug is firmly in place. Also, try out different types of audio. For instance, connect a set top box or video camera to the input jacks and see if any audio comes out of the TV. If you aren't getting any audio from any source, then it may be your cables. Try different cables, and try a different TV.
Audio problems from HDMI connectionEdit
The most common problems are 1) No audio from some programs but audio from others, 2) Background audio but no foreground audio.
Set the SP/DIF to other options and try them out. If you are using a version of the firmware prior to 1.96 then go into setup and set the audio channel to 2 instead of 5.1. The SP/DIF, even though you aren't using an SP/DIF cable, still impacts the way the signal is sent to the HDMI cable.
Another thing that has been discovered is that the HDMI cable that came with the drive is not a very high quality cable. At least twice other users have reported that replacing the cable with a higher quality cable has solved their problems.
Audio problems from compositeEdit
The most common problem with the composite is a buzzing sound instead of the audio. This is typically caused by plugging the video output into the audio input. The yellow jack on the ScreenPlay is the video output. White is left, Red is right, Yellow is video. If you are using an SCART adapter, make sure you are using the right kind of adapter. There are apparently one way adapters that cannot be plugged in backwards (I don't know this from experience, just from reading other people's experiences).