If it does have manual hubs I would take them apart and check that Spring they have in there. My SuperWinches ( which I HATE BTW) had a Flimsey spring in there and just about the time I needed them they snap apart and It sound just like you were saying, "like someone was hitting the front end with a sledgehammer." Where they were just Popping when it felt It needed to. I would check that Spring if you have Manual hubs. I have never run the Auto Hubs and hope I never do. So I cant tell you if it is auto's how to fix them or deal with them. My dad had auto's on his 91 Suburban, they were a PITA... And when you take them apart might as well do a bearing pack while your in there. I LOVE AISIN'S, Need another set.......