Odd stereo issue

[Shumdit]

We have noticed a few times that the stereo would suddenly seem to get louder on the X5. At first I thought it was the speed dependent volume control bumping it up, but now I have heard it happen when sitting at idle, and I think the center speaker (in the dash) is off at times and then suddenly comes on, changing the sound of the stereo. Since this is an intermittant thing, I have reservations that the dealer will find the cause unless there is some TSB on it already, and I was hoping someone else might have had this issue and know what the fix was. I did a search but came up empty.