I've got a Stagg 10 GA 10W RMS Guitar Amp, it has a serious hiss that comes and goes even with nothing plugged into it. So far I can't find a schematic for it, asked Stagg for one but no reply yet. I don't see any swollen caps, cleaned the pots with contact cleaner, the only things I can find so far (with no o-scoe) - are one component, I believe it's a zener diode, gets hot to the touch, and two surface mount components may have fallen off, I don't see them anywhere but they may have fallen out and been eaten by the carpet during disassembly.
This is the amp.