996 PCM Fade and Balance

[5STM5]

I'm having a problem with the audio settings on my 2002 996 PCM, all functions work other than fade and balance, it appears to have set on the midpoint. When I try and change it, screen graphics move in line with the changes I input, but the audio effect doesn't move.
I only recently got the car, so don't know how long it has been like this.
Greatly appreciate any advise.

[5STM5]

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