I am having a problem identifying a noise that appeared suddenly in the left channel of my PAS3. There is a constant low level noise similar to bacon frying, accompanied by occasional louder pops and static noises. This noise appears only in the left channel, is present on all inputs and does not vary with the volume setting. It is similar in character to the sound of a failing tube, but when the tubes are swapped it remains in the left channel.
I made a preliminary effort to find, perhaps, a loose connection by wiggling the tubes in their sockets. No change in the noise. The problem is with the high level board components somewhere after the volume control since the noise doesn't vary with the volume setting. It seems as if a part might be failing; any suggestions where to check first?