I have a Cello Duet-350 power amplifier. It is about 10 years old. It now generates its own gratuitous, random, static-sounding noise. Input level has no effect on the level of this noise. It is not objectionable with listening to Eric Clapton, but it is quite annoying when listening to Chopin Nocturnes. I have disassembled it as far as I could without resorting to a soldering iron; disconnected, cleaned and reconnected every removable contact I could find. I can find no parts inside that are obviously scorched. Does anyone, please, have any ideas about what I might try?