Hi y'all I just got an old Massie Lancer amplifier head (converted from a combo); it's basically a 5E3 Deluxe circuit. The amp makes gurgling static noises. This happens regardless of whether or not anything is plugged into the amp, where the volume and tone controls or set, etc.; there is pretty much a constant staticy gurgle happening. Sometime it goes away, only to return a minute later. Any ideas as to what the culprit could be? Thanks!