06 Sportsman 800. Took it into two shops for major tune ups, and other work…spent about 1800 total for everything…but the one item that I could not get them to actually see/hear or even acknowledge, is the sound of what sounds like metal scraping…Kind of like a "sshhhhkkk" sound when in motion. Also a clacking sound when feathering the throttle. Almost like the smacking of a bad u joint when lightly going from load on the drive train to no load.
The other day I heard a light whining sound starting up when in motion that would increase or decrease with speed. It suddenly made a klunk sound then no motion moving forward. Just rev and no go. I put it in low…and a slight klunk and it moved normally. Put it back in High and it moved forward normally again…but the whine is still there.
I was thinking that maybe I have a motor or tranny mount or something like that is broken causing the drive line to separate under load.

Any other thoughts? I bought this thing cheap about 5yrs ago with a lot of hours and miles on it. Used to be a surveyor’s and he did ride it hard for work on fire roads in the mountains. But now it is a ranch ATV and used for plowing and just general ranch work.
Ever since the klunk and no go it has been sitting. But will need it for this winter.
I checked with another forum and someone said it was the roller cage in the front diff. But this happens in 2×4 as well as 4×4.

Thanks all!