I have a 2008 Dakota quad cab and when I put in 4 wheel drive, hi or low and try to backup it like it's binding up when I only turn to the left or right. I have replaced everything, wheel bearings half shafts, upper and lower ball joints and new universals fronts and backs along with all new brakes and wheel cylinders and calipers. When it does this you can hear a popping and cracking sound under the front seats and has a vibration when going around 40 to 45 mph and disappears around 55 mph but then comes back the faster you go say 65 to 70 mph. Any help would be great, possibly a bad crossmember or???