Hard to say what's going on just from that description but it could be that it's clipping for 1. Might also be too much low end in your kicks, try HP filtering everything but the kick which is providing the low end. Maybe even HP the sub group at a cut off point where you feel the right amount of low end is present.
Don't know why it would suddenly sound distorted at the chorus part of your track, to me that would suggest that maybe you are adding an instrument at that stage which is causing the low end to become muddled.