Anyone know how to tell if the timing chain is worn or stretched beyond the limits on a Suzuki Eiger 400?

I have a service manual and I can't find any mention of it. I'm getting kind of a "whirring" sound that matches the engine speed. Was thinking it may be the timing chain, but I don't know. Had the valve cover off tonight, couldn't see anything obvious. One of the rockers was a bit unusually worn where the cam would contact.