Recently my 08 sportsman 800 has started making a howling noise in the transmission. It is definatly a metal on metal noise and is progressively getting worse. I stuck my finger in the granny fill hole and the fluid is a little dark but normal. It gets a lot louder on deacelleration but is still there on accelleration. It does this on all gears except park and neutral. Anyone have any ideas? The howling is not a steady pitch its almost like a its saying wowowow. Lol please help