I read the thread that was posted and Mike's response to the people having hum problems were basically "eh, you bought those units second hand" and "well, the electrical grid can do weird things to amps". I'm surprised he didn't have more specific actions to try to get the problem solved.
It'd be like Danny telling someone "well, the speaker was working when it left my shop, it must be your amp". I mean, that might be true but it would be a surprise if a manufacturer washed their hands of the situation like that when there's a problem. A better response would be "well, here are the top 3 things that can cause that issue and here's how to test that out".
Personally I've had to deal with hum, both at the speaker and in the amp (tubed equipment, mostly), and I know how annoying it can be. At least the makers of the stuff I have/had were helpful in giving specific advice that allowed me to track down the problem.
Either Mike knows some good ways to troubleshoot these problems and he's just now willing to share, or he doesn't know how to solve it at all and thus can't offer advice or solutions even if he wanted to.
Anyway, I've already said more than I intended to and I don't see this conversation resolving in a non-combative manner, so I'll bow out. Apologies for the thread derailment, Danny.