Dumb Question

So I've owned the E36 M3 for quite awhile and every once in awhile there are 3 short beeps in a row coming from the instrument cluster.

What is that?
What does it mean?

It's so random and at no specific time. At first I thought it was the service buzzer but I'm not sure about that??

I suppose I could look in the old Bentley manual for a simple answer but I figured I may have to dig awhile and one of you smarties would know.

Thanks in advance.