So I installed an lc2i, amp, and 2 subs. Getting weird feedback from subs even when sound is on 0. Figured out it was the ANC AND DEPINNED THE 4 power wires from amp for the factory microphones under the dash. My buddies not happy he wants the Anc to work but doesnt want the sub feedback.
Would installing bass blockers on the microphone leads block out the low frequencies? Thinking of it couldnt hear low frequencies it wouldnt try to cancel them out and with a matching hpf the amp would block higher frequencies from sub.

If you put bass-blockers in the ANC microphone leads it won't allow the ANC to work properly so your buddy wont be happy with that solution.
Car ANC needs to respond to frequencies in the 30 to 250Hz range in order to be effective. If you add some form of bass blocker to the microphones you will preventing the system from doing its job.
Thank you for the additional clarity. Surprised no one has developed an alternative but I'm guessing if this is what the factory sub is used for makes it difficult.
If I pulled signal say from back door instead of the factory sub would that work or are the anc signals sent to all speakers?
Well with a uf133 bass blocker between the lc2i and stock woofer wiring with the ANC mics connected there is no sub feedback and the system hammers. And I think some of the anc is functioning through the other speakers because the truck drives down the road reasonably quiet.

I went through some crap as many of you have with my buddies 2019 dodge ram mega cab 2500 with active noise cancellation or ANC and the Alpine sound system.
He was a pain in my ass about it. He didnt want subs making noise before he started the truck, he didnt want subs making noise when he opened or closed the doors. Hell my vette does it, it's just part of the GTO on the LC2I so I found a good fuse to tie into for remote on. This cured the sub noise while truck was off. The following pic is not my photo but the yellow 20 is a switched 12volt. The other which has a wire is a switched reverse.
I depinned the harness under the dash and disabled the mics and I thought all was well. My buddy called crying my truck has road noise like my old truck. This ain't gonna work. I said turn the music up louder. I searched, and read, and looked through all kind of forums dating back to 2007 Honda Accords, BMW, GM etc and everyone says cut mic wires, depinn this or depinn that. I told my buddy he said no this isnt gonna work you have to figure out something else.
I said I got a crazy idea but no clue if itll work. Someone on this forum said Anc functioned at 30-250hz.
Well a 133uf bass blocker blocks 300hz down. So I installed one between the lc2i and stock woofer wiring with the ANC mics connected there is no sub feedback and the system hammers. And I think some of the anc is functioning through the other speakers because the truck drives down the road reasonably quiet.
Anyway he loves the system I installed 2 12" cvr wired to 1 ohm on a kicker mono amp that certified 918rms, nvx 0 gauge wiring kit, and an Audio Control lc2i. Sub box is a Fox Acoustics Mega Cab box. Awesome box, looks great, and pounds.