The dealership finally called back, it's the front door speakers. They are connected to the ANC. Aftermarket speakers throw the system off. Putting stock speakers back in.
Perhaps a consideration, if you're looking for an upgraded sound system, is to seek the services of a highly qualified audio shop to remedy all of this for you, and still enable you to keep the upgraded front door speakers.
I personally have had experience with this in my old 19' and now my new Warlock that came with the factory Alpine 9-speaker system.
I've got 2100W of Kenwood amps, a 5-farad digital capacitor, all the doors and dash speakers replaced with Focal, and 2 x Audiomobile EVO 2410 subs connected, and they were properly able to tune and time the remaining stock Alpine center channel and 2 x roof speakers, with the factory Alpine amp, to deliver unparalleled sound with zero distortion at full volume.
I can't go past 30 on my Kenwood head unit as my hearing cannot handle the decibels.
I usually listen at 18 just puttering about, then 21 to 25 when I want to really feel the bass and tunes, but when I want to pound hard I go to 28.
30 is reserved for those days that I need my tunes to pump at levels that aren't good for ones ear drums...lol
The three remaining stock Alpine speakers are now acting as merely surround fill speakers and running off the stock Alpine amp. Even at 30 on the dial, there is zero distortion with the factory Alpine speakers. Simply epic sound quality with a more enhanced surround presence.