#1
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.
#2
May just be the glass in the valves expanding on the warm up and contracting on the cool down?
Guitars:
Gibson Les Paul Standard
Gibson Explorer New Century
Gibson RD Artist
Fender American Standard Telecaster

Amps:

Framus Cobra
Marshall JCM800 2203 - 1960A

Pedals:

Crybaby 535Q
Rockbox Boiling Point Overdrive