My Groove gets really warm/hot, is this normal?

Yes.

You may notice that the Apogee Groove can get pretty warm when it's connected to your computer and powered up. This is completely normal and it doesn't mean there is anything wrong with it. Audio quality with very low noise and low distortion requires using more current and this creates heat dissipation. In order to get the amazing audio performance it does, Groove requires a decent amount of current, and because of this, it will definitely get warm. If you connect your Groove to your computer and it is recognized by the computer, plays back audio, and starts to feel warm to the touch after a while, this means it is working as expected. If there were a hardware issue with a Groove, it would either not power up at all (which means it wouldn't get warm) or it would power up, but not play audio.