xxrap985xx

i just installed my subs in the car and when i turn the volume up on the idrive the subs cut out.. and the second i turn down the volume they go right back on. the amp doesnt go into protect or shut off .. did anyone have this problem after installing a sub system with their car.i checked and double check everything on the install and i did everything right. i put the gain down to half way and it still did it. the freq and everything else is all right. does the logic7 system have problem with aftermarket systems. i have two polk momo c.500 powering two polk sr124dvc subs. the subs will rms 700 each and the amps are tested at 14.4v with 670 watts. i have a 545i with a logic7 system. any help????!?