I have a 2001 Polaris Expedition 325, recently the 2 wheel drive stopped working. It will drive in 4 wheel drive but the back makes a bad grinding noise. Also, if I put it in neutral and try to freely spin the back tires it also makes the grinding noise. Anyone have any idea what this could be?

 

Could be one or more of several things...hubs stripped, axle splines, ring gear splines, bearings toast, etc, etc... The ONLY way to know/find out is to tear it down and see.