I once had the same problem, I was shooting outdoors, quite far from the city, so I had to try to fix it by myself.
I found out that it was something into the CMC6 that was moving.
I first removed the capsule.
I discovered that the little screws that keep the CMC6 closed do not hold it like ordinary screws, but they are in the inside, pushing out on the casing, keeping it still.
In fact, if you try to screw them clockwise they will keep to go into the mic and they finally will fall into it.
If you see one of the screws missing, that's probably what happened and you have just to open the CMC6, take the missing screw and put it in its place.
(First post, hello everyone!)