1998 Z3 M Radio Info Needed

[MVT]

I have a 1998 Z3 M with the stock business class radio. The whole audio system is stock.

Recently, it became hard to adjust the volume.
I could just turn and turn the knob and it 'might' eventually change the volume.
Then one day, while riding with the top down and the volume turned up to compensate for the wind noise,
it got stuck on high.
Now no amount of dialing on the knob changes the volume.
This volume is way too loud when riding with the top up.

Okay, so I figured the volume knob had a short or something.
So I went online and purchased another, used business class radio to replace it.
Same year, same model. Just unplug old radio and plug in the new (used) one.

Well, I did that, but guess what.
The volume on this radio is also stuck on way too loud.

I'm 93.5% sure it's just another bad knob on another bad radio.
But . . . . since I'm no expert on Z3 M audio systems, maybe there is some other reason.
I have no clue what other reason could cause this, so figured I would query the community to see if I'm missing something.
I know auto electronics can be as mysterious as computer stuff to try to figure out sometimes.

Thanks for any assistance or knowledge you can impart.

(before I go out and buy yet another radio)
(and I have put a replacement business class radio in my 1984 318i with no problems - plug and play)

MT

 

[137699]

Swap the radio with your 318i and see if the problem moves?

 

[MVT]

Now why didn't I think of that ? ? ?

Thanks for the smack to the back of the head.
(That's how my Pops used to tell me when I was blind to the obvious)

I'll give it a go and come back here if it continues to do the same thing.

Thanks again.
MT