Hello yall. I have a 13 850 making some bearing noise from what seams to be the rear pinion area. I recently acquired the machine and went threw all the fluids replacing with amsoil. At about 15mph and higher I get a growling noise from rear diff under acceleration that disappears when I release throttle. Should I get that amsoil otta there or is it to late? Or maybe I'm being crazy but its loud and doesn't seam right. No play in driveshaft or any leaks.