Bolt EV Audio Volume Fluctuates

My radio sound volume randomly fluctuates between two levels. It switches from one volume level to the other and back again for no apparent reason. Both levels are adjustable - i.e. when the louder volume is playing, I can change it using the volume knob (if I catch it in time, before it switches again), and the same with the softer volume. If can set them to be equal and the problem disappears temporarily, but returns intermittently whenever I change volume again.

At first, I thought it might be caused by Android Auto, or the Bolt's Auto Volume feature, but I turned both of those off and still had the fluctuating volume levels. However, the problem does go away when I turn off my phone's Bluetooth (disconnecting it from myChevrolet). I'm guessing that for some reason, the Bolt sound system has a separate volume that applies only when a Bluetooth device is connected, regardless of whether sound is coming from the Bluetooth device (Note that I am NOT using the phone as my audio source when this problem occurs, just playing FM on the Bolt's radio), and perhaps the Bluetooth connection drops occasionally, enabling the volume to shift to the non-Bluetooth level? It makes no sense, and I don't see this in the manual, so it really is just a wild guess based on the radio's behavior. And really, the Bluetooth connection should be very stable inside the car, I would think.

It's of course very annoying when the FM volume intermittently jumps from 10 to 20 and back again. Any solutions, explanations, or similar experiences would be greatly appreciated!