SX4 Audio Problems

I'm playing two separate programs at the same time on separate channels thru my sx4. However, the audio from the program on channel 1 is coming thru on channel 2. I stop the program running on channel 1 and channel 2 still has no audio, nor do channels 3 & 4. Is there a setting that is causing this? All files on the SX4 have audio, and all the equipment is hard-wired correctly. Channel 1 is the only channel that is getting audio. The default input for all channels is a carousel and it works fine.