I hate my obsession

[GoldenVulture]

I did just that, fearing a grounding issue between some components squashed together when the chassis was reseated, but for now things appear to be okay.

That's good to hear. I had a cold solder earthing  that only showed up under loud volume. Hit a full chord and I'd get a distortion/crackling at certain frequencies, mostly mids. It took ages to find it by resoldring  solder points. I've had crackle and distortion problems in the past from dirty valve pins.