Guys, it's not the foam causing the rattle.
If your foam has rotted away, and the element is freely moving inside, then yes there will be some handling noise and the foam will need to be replaced.
Contrary to what others have said, replacing the foam alone will NOT remedy 'baby rattle syndrome'
Have a listen, here's a customer's mic, we took samples of kick before and after it was repaired by our shop.
Note, the foam of this microphone was needing replaced only as a preemptive measure, it was NOT the root cause of failure.
I suggest replacing the foam every 5-10 years BEFORE it rots out.
"Microphone technique is an art and the ear of the listener is the critic"