Gliderguider...I hope you realize I was jerking your chain :)
Yes, engineering does have a lot to do with it. Many years ago I built a Heathkit preamp. It had what seemed to be miles of hand-twisted and shielded wire, some of it encased in spring-like outer sheaths. It was very difficult to construct. It hummed. The next preamp I built was a Dyna Kit. It had not a single piece of shielded wire, was easy to construct, and (almost) dead silent.
The good tube equipment that I have heard does not hum enough to be a problem. (Audible only with volume up and no signal). On the other hand, I have never had any hum from SS equipment, except when there was a ground loop needing correction. I think this is because ss circuits run at low impedance, and are less susceptible to magnetic fields.
