2013 D4 HSE Audio mode Phantom switching

[Scottyj11]

I have a 2013 D4 SDV6 HSE with stock (premium) audio system. I mostly use Bluetooth connection with my phone and have noticed recently, occasional Phantom switching from this mode to Auxiliary mode. I can confirm that there is no cable, plugged into the auxiliary jack.

Any ideas why this might be happening? Or how to address it?