hispls 5,000+ posts
CarAudio.com Veteran
That is very probably the resonant frequency of your vehicle and will exist with any subs/box you put in there. Most of us in SUV or other full sized vehicle find that point between 45 and 55hz, CRX is up close to 70hz. It generally works out to the distance from the subs to the windshield divide by the speed of sound divide by 2. You're probably getting a bump at half that frequency as well but it's either helping or at least not enough to jump out at you.there are certain notes in certain hip hop songs somewhere around 80hz that will jump out as just way over the top.
As you say, crossing over a tad lower is an easy fix and I'm happy to hear this all came together to give you enjoyable music.
Finally, if that's an old Planet Audio 2 channel I can't believe it's driving 1 ohm per channel. On the bright side, you can find 800W in class D easy enough whenever that breaks.