Just a guess, but the primary chain tensioner might be hanging up allowing the chain to flop around a bit. The clicking could be the chain scraping the inner primary.
Might try running up to 30 - 35 mph in 2nd, then backing off suddenly. You really can't see much in the primary with the clutch in the way, but it won't hurt to pull the inspection cover and shine a flashlight to see how loose the chain is. Might be able to jiggle the tensioner with a bent clothes hanger. You might also have to pull the outer primary cover but that will cost you a gasket.
May need a fluid change, and if so check the plug for aluminum looking grey gunk.
Noise tends to travel, and it might be a lifter not pumping up right away or even something in the valve train. Harbor Freight has an engine stethoscope for cheap that will help pin down the noise source.
Good luck, and let us know what you find.