I have a pro stock frame (a PT57A w/ FXP pj) and I got the same problem going on with it. It is the long strips of lead tape under the bumper, and the broken pieces of lead tape are making quite a rattle now. It happened before, like 6 months ago. At that time, I took off all the grommets, then tried to shake the tiny bits of lead out of the grommet holes. But when I started swinging and banging the grommet-less stick, the rattling sound disappeared on me!! Nothing came off...
So, did put the grommets back on (which putting back them on was a REAL PAIN IN THE ASS, partially due to me not being used to putting these on, I guess. And partially, I heard PT630 type grommets are tough to deal with even with experienced stringers. And my forte is with putting on a condom, not the grommet LOL. Anyways, when I was done with putting the grommets on finally, the disturbing rattling noise instantly came back!!! It turned me crazy. Now, 6 months later, I can clearly hear many more pieces of broken piece of lead tape strips every time I swing the stick.
I think I will have to put new grommets, and also must put new lead tape strips on the racquet as the ones on it kind of gotten old and can easily break. It will be lots of work, and I will have to be very careful so as not to change the balance of the stick, as it is a special frame...