I have a 2004 sportsman 600 twin and when I accelerateI get a really loud high pitch whine. It continues until I letoff the throttle then it completely goes away until I get back on throttle. The noise really gets loud about 25 mph all the way to 50 mph. I took it to the dealer and they took apart the transmission and they could not find anything wrong. They thin the transmission is still the problem and want to put a new one in. Any thoughts. It has 156hours and 2600 miles.