I have a 2007 JD 797 zero turn with about 360 hrs. When I engage the PTO, there is a loud what sounds like metal on metal noise coming from the rear of the mower. The blades are slow to get to speed and they are easily slowed with cutting grass. I'm guessing a bearing is going out. Any suggestions? Is this easy to change out or do I need to take to a dealer and have them fix it. Any help is appreciated.