Engine Knock

So yesterday I was riding and all was well. On my way home from the gas station I notice that my bikes idle had increased to 2k instead of the usual 1k. When I got home I let it idle in my driveway and it was knocking at idle. The knocking goes away as long as I'm riding it and its above 2-2.5k rpm.
This knocking occurs only under 2.5k and it knocks while cold and hot. How should I diagnose this problem? Is it the cam chain? Exhaust leak?

Typical possibilities would include development of an air leak, perhaps from worn or cracked carb holder, loose clamp holding carb inside carb holder, bad vac plug, crack in vac hose to petcock, etc.

Is the EPA clean air paraphernalia still fitted?
If so, the related hoses and connections may be the source of an air leak.,

Good Fortune!