Its the epoxy in those gaps that is cracked and loose. When you add pressure to the sleeve by bracing or drawing the "stub" end of the billet shifts from one side of the sleeve to the other making that crunching sound you hear. Fear not, it wont hurt a thing, but its damn annoying isnt it? I woudl try to get a thinner epoxy that will flow down in your gaps and fille them. Let it cure for at least 4-5 days. It takes much longer than the wrapper says when you fill deep gaps with no air flow.