Car aux not working without 12 volts cigarette liter plugged in

A weird problem has recently developed on my KA.

When my phone is plugged into the aux without the charger the sound sounds incredibly strange, really quite and tinny. This corrects it self when the charger is plugged in (from the 12 volts). I have changed phone to see if this corrects the problem.

There is also a lot of whiny noise coming from the stereo in aux mode with higher revs, I have tried a inline aux ground loop, to no effect.

Interestingly if the plugged in phone charger touches any metal bodywork in the car the aux then works fine?

Is this a ground issue? Is there a way I can fix this? It very suddenly came on.