my 03 660 grizz makes a strange noise when you let off throttle.its a metal rattle sound way more when hot goes away when you give a bit of throttle or engage 4 wheel drive?mostly when going down hill and bumpy.clutch has been serviced.

 

Mine had a noise like a clunk or rattle , I believe all grizzlys have this noise , did you just buy your Griz ? cause mine did it from new in 04 ,If you grab the front drive shaft you can wiggle it back and forth or side to side and it makes a clunking or rattle sound I found that strange on a new quad . Also if you have a plow mount plate on the bottom ,check to make sure all the u-bolts are there.and tight or you will also get an iritating noise.Dont forget to check the exhaust shield.good luck.