said by AndrewG2:The capacitor at the bottom of the red line has it's wrapper coming off.
How random is the random hiss, does it turn on constantly for 15 mins or more, or is it more like psssssssssssst stop psssssssssssssst etc with random length bursts and pauses over a few minutes?
If it's the second scenario, I suspect it's RF breakthrough from taxis, police or utilities radios where the carrier is breaking through, but modulation is not strong enough to hear any "signal". i.e. distant signals a mile or so off.... however, if a cab stopped right outside his house to check in, it might bleed through audio, (and blast him out of bed at 3AM if he left it on and turned up )