Xanadu1209

I recently acquired a 130XE that's been sitting in a shed for years. I powered it on and everything seems to work fine except for the audio. It just outputs a nasty high pitched static sound. So far I've just been using it with the audio cables unplugged. I do not have the RF modulator to see if the sound comes from that output as well. I've dug around on Google and can't find any helpful information on where to look for problems. I can't find any obviously bad components or solder joints. The board appears to be in good shape. I'm going to take it to a friend's house to use his troubleshooting tools but I figured I'd see if anyone has any recommendations for where to look for problems. Thanks!