I've got a strange noise under center of my quad and I cann't find what it is, It has a knocking noise that picks up with speed and it doesn't do it when it is cold, you might have to ride it 20 min. or so and then it gets quite loud, even some one next can hear it. It seems worse under a load even turning slow makes it knock. I drained tranny and found almost nothing on magnetic plug, I've checked chain and spockets close, I've checked primary and secondary and changed belt, still does it? It is a 2000 scrambler 500 4x4 with 800 miles, never jumped it or anything too crazy. It starts with a rumble thats on and off and is speed related. Let up on thottle and it quits, but problem isn't going away and I don't want to run it and make it worse, I hate to take tranny apart if that isn't it. I hope someone knows what this is and can point me in right direction, thanks