Hi, I have a 743B with 3700 hrs, everything works great, but when I run the machine at 3/4 to full throtttle and drive it around I hear a metalic grinding noise comming from the left side, maybe both sometimes. Less than 3/4 it does not seem to be noticable. Sounds like a chain grind when turning or full speed ahead, also when going down hill or if you hit a bump, its like the chain "catches up" and makes this sound. I thought that this thing had auto adjusting chain? or is it just plain stretched out?? And how do you adjust it or fix this? Thanks!