Headset Humming on the laptop?

I'm using an external USB sound card on the laptop and have connected a headset. There's a permanent hum, but as soon as I put my hand over the USB port, the hum disappears. I can't explain why that is. Maybe someone knows a solution.

Bad shielding or a slight short circuit.

I already have to connect the headset via the following adapter and it is not recognized. Sound is played through the headset, but the microphone does not work and is not displayed. There's a combination socket on the notebook.

https://www.otto.de/...=944868656

Try a different headset maybe on loan.