subwoofer rattles like hell


hi, it's a mirage bps 150i. it is bipolar, has two 8" woofers. supposed to be very good. this is my first sub. i have a 90 watt amp. it is clean strong power. when i turn the gain past two the left woofer rattles like crazy. like wod smakking together. is the speaker blown or can it just not handle the power coming from the amp. is this refered to as clipping? please advise. thanks in advance.
brash
Alrau1, it is a push pull configuration so i think if the drivers are pushed too hard it might overload just one of them. what you say does make sense though. problem being i bought it used and it seemed to work pretty good until i made all my adjustments and break in time of the other components, so manufacturers warranty is not an option. it, sadly, was a stretch for me to purchase even used (i'm saving for a bigger house) and i fear repairing will be out of the question. i guess i was hoping for a different answer but thanks a ton for everybodies input!
I just look at the owners manual. The sub has BOTH Hi-level inputs AND outputs with the inputs being the BOTTOM row. Verify your connections, just covering all bases.
Otherwise contact the manufacturer. (go to Audiongon's home page and see manufacturer's list link on the right side for contacts and website).
Good Luck.