I'm working on my dad's machine. The other day he started noticing a clunking noise while operating the machine. He said he could actually feel it when it was making the sound. He also said it came on quickly. I checked the drive chains and they all have a considerable amount of play, enough that I can hear them contacting the chain case. I'll be changing the drive chains. The sprockets look to be in good shape but we haven't completely drained the chain case yet to see the entire sprocket. I checked the axle bearings for end play and found none. Is there anything else I should be checking that might make a clunking noise while turning? I don't know if a carrier could be bad as well? I can't feel any wiggle in the drive sprockets but I won't know for sure until I get the chains off of the sprockets. My dad doesn't put a lot of hours on the machine each year so I'm not really worried about putting new chain on old sprockets. I think I have my bases pretty well covered but suggestions on other things to check are appreciated.