Noises like that suck to track down sometimes, especially when they are deep in the dash or a door panel. My wife's jetta had a couple that I could never find. I figured if I pulled the dash apart I would probably break clips and create more noises. Good luck to you if you dig into it. If you only have one annoying chirp on an 89 you're doing alright.
There is a lot of good info on this site too, might have a look.
The Ranger Station - Technical Library