I think I might have been the first to report mild hum from the neo stuff, having TV36ipals that shipped day one along with Hop's. It's only noticeable if you are standing 1-2 feet from the sub, and I actually only hear it at all from one of them. I didn't think to mess with the gain knobs, but that could definitely be the difference. When Audyssey had me set the gain levels of the subs, one needed a little more on the knob, and that's the one that I can hear mildly humming. The sub with a lower gain setting and no hum just happens to be in a corner, so that would explain why it needed less gain than the other one.
If I was planning to keep the subs long term, I would definitely lower the gain knob a bit, even if it means Audyssey coming back at -5 instead of my preferred -10ish. I can always boost in the miniDSP if I want to, and losing the hum would be good for peace of mind, even though it's not audible farther than a few feet away from the sub.
It looks like this on Spectroid - I turned the receiver on about halfway up the graph, you can see it on the ~-70 db line or so.
It also sounds the same whether there is a signal cable connected or not, and each sub is on a fully dedicated circuit, so I don't think it's anything related to a ground loop, even though the hum is centered around 59 Hz. I think it's just the nature of the drivers and the amp gain setup.
I'll reiterate, since I know there are some weirdos out there who love to hate PSA and will run with this like they ran with the false rumors of chuffing from an abused V1801: The hum is completely inaudible from any reasonable distance from the sub, and can probably be completely eliminated by lowering the gain on the amp. It's also literally the ONLY small issue I've had with the TV36ipals. Their actual performance has been nothing short of astonishing, both in quality and quantity of bass. I really wish I could keep them, and I'll 100% pick up another pair down the road when I move to a bigger house.