Audio balance adjusting itself

The audio balance out of my Mac keeps adjusting itself to the left and right - It's driving me crazy..

I think it happens every time I connect- or disconnect headphones etc. not just at random.

I don't have the problem when I use my Steinberg audio interface, it's only when I use the internal speakers or headphones etc.

I have no idea of what causes the problem, it might be something I do that I'm not aware of.

Does anyone know what I should do?