Two of the 5 amps I've owned do this. (B-52 ATX-100 and my Triple Rec). While they're sitting in standby mode, and also right after I turn off the amp, they make a chirping type of noise, like a cricket. Is this normal? None of the lower wattage heads I've had do this -- only the big boys. Is this a sign of a dying tube or something? Everything sounds fine.
May just be the glass in the valves expanding on the warm up and contracting on the cool down?
Gibson Les Paul Standard
Gibson Explorer New Century
Gibson RD Artist
Fender American Standard Telecaster


Framus Cobra
Marshall JCM800 2203 - 1960A


Crybaby 535Q
Rockbox Boiling Point Overdrive