Ahh awesome, so this treats the audio rather than the USB. Potentially more usecases for this one. For the convenience of other burgers here's the American link.
Some GLI's are trash. You bought a well known one? I bought this one for my Switch, working wonderfully.
All of that does sound like ground loop issues. I had those too and there was a ever-present whining sound when the engine was running. I bought this:
https://www.amazon.com/gp/product/B019FC6ZQQ/ref=oh_aui_detailpage_o02_s02?ie=UTF8&psc=1
This is plugged between the tablet and the amplifier (not using USB DAC but an amp that takes analog input).