THANK YOU SO MUCH!!!
I purchased a used 2013 C-max with the premium audio package and was so worried that the alarmingly loud sound was going to be a big issue that needed servicing. After browsing on forums I had a sneaking suspicion that my problem was in fact the sound was the ANC system.
Thankfully I found this post, got nice and cozy with my car, pulled the plug and *chefs kiss*
No more deafening sound, just slightly more noticeable engine noise! YAY!