I have ported box tuned to 35hz my understanding is half octive below trying to set at 27hz but get a humming anything below 80hz that's like 50 some hz away.
I don't know if humming is right word but best I can subscribe and lower than 80hz the bass I can here coming from the back of car and still up front tried lowering gain but no . When setting gain it has to be 80hz no lower or I can't set it.
Humming would tend to mean that something is driving a signal into the amp. Do you have any mains powered equipment connected to the vehicle?
It's a Nissan maxima sv with the Bose with navigation not using any of the Bose equipment it's still in car just not turned on so hu I have is in armrest ran seperate power wires and amps and everything. Not sure what you mean by main powered equipment you r talking about
Do you have any equipment plugged into the mains supply (60Hz 120v AC) like a scope or signal generator?
Those may not be 'added' but they may be used in testing.
Do you have a meter that can read frequency?
Do you have a meter that can read frequency?
Alternator, heat/AC blower whine due to poor grounding? Just 'knee jerk', 'grabbing at straws' here 
I hear you. Tested ground from amp to battery , no engine noise or anything from other speakers. Checked resistance on subs they are fine used 9v on them that checked fine . It's as soon as I play a test tone they start making noise before I even touch the Gain and subsonic is at 10hz lp filter all the up everything flat 0 what not. With gain real low the bass sounds like it's coming from up front but I also totally here it coming from the trunk like not even part of the system. Idk bad subsonic dial, something with amp or Hu tried other Rca's no luck .