I had a faint thumping sound in the drivetrain once in awhile after doing a little offroading in San Felipe, but now the thumping is definitely worse after doing the suspension. Recently I drained the diff oil to see if anything was in there, but it looked clean. Are the U-joints, carrier bearing or differential going out? I also wondered about the transfer case. Everything seems slop free and noiseless when spun by hand. What tests could I do to isolate?