Why do the sensor signals bounce around even when the device is not on my head?

This is expected behavior. The sensors on the headset are able to pick up environmental signals when it's not on your head. The 3 sensors work together to cancel out any environmental signals when getting a signal check for training.  That's why it is important to make sure that when training you're not situated too close to WiFi routers, that your headset is not charging while in use and that you're not holding onto or close to devices that are charging.