hey y'all...i recently got a mcgohan p.a. at a sale for a buck...it works, but when you turn up the treble, it reveals an annoying hiss, even with all volume knobs turned to zero. i replaced the one carbon comp resistor it had, but no change.  it has a small (.001uf)ceramic cap as the last component before the treble pot...any chance this is the problem?  any suggestions?   thanks!