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

curiousjim Details Discussions Posts This discussion Message User 4,153 posts 04-27-2023 at 01:38pm Copy Comment URL Report Comment Edit Delete @tomask6 Airplanes have so many electronic devices working the hum could be many things, but I’m guessing when you hold your device, you are grounding it. Apple or many others offer external batteries. I have a couple of them. The Apple one is about the size of a deck of cards only square and the No name one is the width of a deck of cards only almost twice the length. Either keeps my iPad charged for 36+ hours, when doing a lot of video calls. All the best.