2018 TLX aftermarket sub and amp issues
 

I have a 2018 TLX with the ELS audio system and wanted to get a little more low end bass because the factory sub leaves much to be desired. Didn't want anything super powerful, just a little more thump. Bought a cheap 10" sub with built in 300W amp. Instruction state that the amp can take low or high inputs. Just cut off rca jacks and wire in high signal. Tapped both rear deck speakers and wired into amp. When I first turned everything on, nothing. Amp had power but sound. Ended up cutting one of the input wires coming from deck speaker and viola sub jumped to life. Tried swapping polarity on that input thinking maybe they are 180deg out and canceling each other out, but that didn't work. As soon as you hook the second input wire up, sub goes dead. So, I have only one input and amp is working. At idle and cruising speeds amp plays ok. Seems a little weak but ok. Problem is on acceleration, I get a feedback/interference coming through the sub. Imagine how a ground loop whine sounds but very low and rumbly. I have installed a number of sound systems in my life but have never encountered this. This is however the newest/nicest vehicle I have tried to install on. Any ideas? Could it be the ANC system making the rumble and why would the second input kill the sub? Any info would be great.

Just to clarify, did you really cut off rca's and go high level? Are there two sets of inputs on the new amp?

Most of my problems ended up being the ANC system but never could get to sound right. Just bought cheap crap. Ripped all out and got my money back. Left ANC unplugged and factory sub is good enough.