Might help narrow it down if you can give more info. Does the grinding happen all the time, only when in motion, only during acceleration, only when turning...? Does the noise sound like it is coming fron the front, rear...? What does the grinding sound like? Have you checked to make sure the drive shafts are not rubbing the cross members or skid plates (if you have them)? Have you checked the brakes...the back plate may have gotten bent during the install? Did you change tire/wheel size at the same time? They could be rubbing the wheel wells.