Descent Subwoofer Problem

I have 2 Descent subs from Martin Logan. They are about 2 months old. The one sub went back for repair 3 weeks ago for a huming problem. I just got it back a week ago and I tried to play some deep bass music. The sub that just came back from the hum repair is rattling like the voice coils are hitting the magnet. The other sub is fine. They are both set at the same settings 5.5 on the volume and 3.5 on the 25hz knob.Dose anybody know what is going on with this sub? I will call Martin Logan on Monday and talk to Jim Power again. I just wanted to check with you guys if there is something I can do.

Thanks
Russb