I brought some white all purpose grease from auto parts store (comes in a can) and greased the roller track at the top (liberally) and the door connector points. (the female points on the frame) and that takes away the noise for a month (thumping and rattling). I am not sure why. I just followed a post/advice. I think it may actually cause a buffer in the door track, since it is pretty thick stuff.. However, the grease eventually dries up after a month and you need to reapply. I understand it is not intended to be the most refined, sophisticated vehicle, but a workhorse. However, the nature of the problem is more a result of a little sloppiness in the design. A couple of millimeters off the track width would have solved the problem with a tighter fit for the roller. Still like the vehicle but there are some annoying quirks for sure.