Have you replaced the batteries? Try that and if it doesn't help, take out the preamp and make sure all the solder connections are solid. It might also be the jack. I had a problem with my '98 Cirrus years back where the nut inside the cavity holding the jack in was loose, and I had output problems until I tightened it.
Hope this helps!
U.S. Peavey Cirrus Club Member # 21