That takes me back to dingy rehearsal rooms, rubbish gear, hired amps and tons of youthful enthusiasm... and the local Taxi radio's coming through the speakers when you weren't playing. I remember one time picking up, what sounded like Russian radio!
Check your leads from guitar to amp, and any pedal leads. This is usually a symptom of unshielded leads. If it's your amp, then maybe it's time to have it serviced as well.