The last time my wheel started the "shimmy" my upper and lower bearing retainers came loose. unfortunately I had to drive 25 miles to get to my tools (was lazy when I prepped) and by the time I got home one of my upper bearing was destroyed. Torque all 16 of those 17mm nuts at 80foot pounds and go from there. if it's not gone (vibration) buy Marlins new axle seals and tear it down I bet you will find a bad bearing if they are aren't loose
