If you're installing aftermarket subs in a TL and you're using the factory sub for signal you may run into feedback playing through your aftermarket subs. The ANC (Active Noise Cancelling) system has mics which pick up interior noise and use the factory sub to play the opposite frequency to lower interior noise. You can disable the mics in the headliner or just remove the ANC module which I find is much easier.

The ANC module can be located underneath the center channel speaker in the dash. Just pry out the speaker and remove the two 10MM nuts holding the module. Unplug the module and put the speaker back, no more noise.