The switch that you press activates a relay - somewhere - which powers
the window regulator (motor). If you're lucky, the relay is shot and $25
or $30 will fix it, otherwise the door must be opened and the regulator
replaced. My 116 needed a regulator, also its aluminum window tracks
replaced as they were bent.
If you can locate the relay - possibly at the site of the buzzing -
there may be other, identical relays nearby - for other windows, sunroof
etc. that you can swap and so determine which is the defective relay and
close the window if the problem is only in the relay or, learn that the
regulator is the problem.