Clutch Questions and Funny Noise

Hey everyone, I have two questions/problems I'm looking for help with. I have an 88 FourTrax 300 2wd that I've had for a little over a year. Bike runs great, always starts never had a lick of trouble until lately.

First problem is, I think the clutch is slipping but I haven't been able to figure out how the clutch system all works. My problem is not so much on take off but at higher speeds or when pulling a heavy load the rpms raise but I don't seem to gain any speed like it used to. I have adjusted the clutch with the screw on the side of the engine according to the service manual I have but it doesn't seem to make any difference. I did not notice this problem until after I pulled a drag harrow around for a while last summer so I think I probably glazed the clutch. However, what I don't understand is.. Are the two clutches? a centrifugal for take off and another one for shifting? I'm not sure which one would be in need of service.

Second Problem is a funny noise that the engine has made ever since I've owned it but never could figure out what it is. The noise sounds like "pinging" in a car engine combined with a rattle. It sounds like its coming from the top end of the engine and only happens when you drive at a constant throttle with a light to moderate load. Under WOT I don't notice it and at idle I can't hear it. My thought was cam chain? but I have no clue.

Anyway, sorry for the long post but, thanks in advance for any help.