I checked the slip joint and it was tight as new, cleaned and greased it and it didn't make any difference. I put bigger bolts in that fit the oversized holes in the bracket for the rear end. I found that standard sized bolt instead of metric fit the holes perfectly. I used grade 8 and torqued them to the spec for the bolt. The aftermarket rear end had undersized holes that I reamed out to fit the bolts. It does not flex at all and seemed to quiet it down a little. I only have one last thing to try at some point, the axle on drivers side is loose at the cv joint. I will live with the noise for now. I did find one thing the made the noise go away. I put 300 pound tractor weights in the bed to have traction enough to back hopper wagons full into the barn. The extra weight stopped the noise completely. I did find I could use only #100 and it worked also.