If something inside a capsule head can make a noise like that, it's moving and bumping up against something hard--which means that it's already coming apart in some way and is only likely to damage itself more.
I'd say send it to Sennheiser USA (if you're in the U.S.) for checkout and an estimate. Past a certain point, capsule repairs for Neumann microphones become capsule replacements, which are very expensive. You may have a chance to stop the problem before it reaches that point.
--best regards