The Beyerdynamic M500/M260 is a great sounding hyper cardioid ribbon microphone. They employ a small geometry ribbon, with an acoustic chamber behind the ribbon that extends into the base of the microphone to alter the microphones pickup pattern.
In many cases, there is debris in the magnetic gap, which can take the form of flaking glue, or sometimes metal contamination. In this example, flaking glue is preventing the ribbon from proper movement. Unfortunately, in most cases the ribbon needs to be replaced in order to properly clean.
This Cascade Fathead came in for repair sounding not very happy.
A peak inside shows a ribbon mic that was likely subjected to some close proximity, loud guitar amplifier.
A closer look at the excursion shows what happens when ribbons are subjected to too much air movement. The ribbon is pushed against the screen to the point where the corrugations are removed, and the ribbon takes on the pattern of the screen it is pushed against.