My Max IV suddenly started making horible grinding noise when turning hard left or right. If I make gentle turns everything seems great. If I try to turn in a circle while standing still it sound like something is going to break. I lifted it up so the wheels all hang loose and the chains and sprockets look fine. All the wheels turn nice and smooth. I had tracks on it. Now I still have the track bearing extensions on each axle and the 26" wheels. Any thoughts of what I should look at next?