Airplane Seat Power Ground Loop?

I’ve experienced the following on several flights, 787’s mainly:

I plug my laptop into the seat power outlet.

I plug in my Audioengine D1 dac.

I plug headphones into the dac.

If I am HOLDING (touching) the dac in my hand, it sounds great.

If I do not hold/touch the dac, there is a hum/noise.

The hum disappears if I touch the dac.

The hum disappears if I unplug from seat power.

What is going on and how can I stop this?

My computer battery cannot hold up enough for long-haul flights and it's impractical to hold it all the time.

Thanks.

Thanks!

tomask604-26-2023 5:37am

tomask6 OP Details Discussions Posts This discussion Message User 43 posts 04-26-2023 at 10:45pm Copy Comment URL Report Comment Edit Delete clearthink the problem does not occur outside the airplane ie when it’s plugged into a land-based power source. Also, I used another dac (a THX one) and got the same problem except the problem doesn't go away when I touch it.
tomask6 OP Details Discussions Posts This discussion Message User 43 posts 04-28-2023 at 06:49am Copy Comment URL Report Comment Edit Delete Audioengine wrote me back said the airplane power isn't properly grounded so I am the ground. Will try the wristband. Incidentally, unrelated to this post, I flew a United 787 last year and when my bare arm touched any metal surrounding the armrest, I swear I felt current running thru it to the point where it got uncomfortable after many hours. We're talking 15 hour flights here, not short hops, so it's nice to play locally stored hi res music on my laptop while I work.