There's really no reason for a noise that's happening at 1" of excursion to happen just because oif the box. You're not stressing the sub mechanically, and it seems like you have plenty of power available to push the subs pretty hard...you're just not able to for some reason, so in my opinion there is something mechanically wrong with the speakers. Or maybe you have them wired to 8ohms and are pushing the amp really hard to get some power to the subs? That could be why you're not getting much excursion before they start sounding like arse.
But those subs are capable of about 3" of mechanical stroke before they start to want to destroy themselves...judging by your vid you're not near that, and it actually sounds like a misaligned coil scratching the motor.