[morzh]

yes it potentially can be the switch itself if it bounces a lot.

here's the test (somewhat dangerous...that is requiring observing some safety, so be careful. Use an isolation transformer and never hold two wires or a wire and the chassis with both hands at the same time....you know the spiel);

Desolder one wire to the switch, turn the switch on and keep it on, so you can have the volume where it works, and use that desoldered wire to make/break connection. If the sound persists, it is not the switch, if it goes away - it is the switch.