Ha, thanks, awesome insight coming from "Ungrounded Lightning"!
On some of the systems we put a neutral current eliminator to try to "fix" the 60Hz buzz coming off of improperly grounded computers. I think it was overkill for what we were doing, because by that point we had given up trying to use internal audio cards for some of our rackmount computers and were using SoundBlaster Live! USB audio dongles where we couldn't use digital audio, which made most of our system noise problems go away. But it would be nice to have an affordable NCE for some applications, like being able to run amplified speakers from my phone or laptop while they're charging.
In my car I get alternator noise if I try to charge my phone while it's playing music to the aux input. I can make it go away by using a Qi wireless charger instead of plugging in the USB directly... with the added bonus that I'm not fiddling with trying to plug my phone in while I'm driving. Another way to make the alternator noise go away is paradoxically plugging an inverter into the accessory port and using a standard 120V AC wall wart USB charger with the phone. (shrug). Next car will probably have a bluetooth head unit, which I'm sure brings on another set of annoyances.