Could be as simple as the fact that more care is taken "on stage" with placement/cables/quality of components than when "in the shed" interested to hear how you get on.
As Ecca says especially with single coil guitars there's all kinds of interference just waiting to show itself, the strings do make quite a good aerial you know
Can you be more specific about the noise Dave ?
Is it mains hum, is it constant or modulating, is it rustling/hash type noises, is it a hissing type noise ?
You could try pulling then re-seating the valves in the etap, costs nothing & might just throw up something
Dick.
You didn't mention the DeArmond pedal, good to hear there's some progress.