I LOVE my Magnus Stinger Buzz Cuts!

Having said that, 2 of the 6 that I have....rattle! What's up with that?? I've tightened the blades and the broadheads themselves (on the shaft), but when I tap the arrow on my neck (holding the fletched end), I hear a rattle. I can even hear it a bit when I draw those 2 arrows. I've switched the broadheads to different arrows, and the rattle remains...so it's clearly the broadhead (as opposed to the shaft, insert, nock, etc.).

Any ideas?? I can't seem to fix it!

Thanks!