Tapping/knocking sound

[Chamberpains]

This may sound far fetched, but, are you hearing the noise only when driving? I recently had a rear differential get water in it and it took out the carrier bearing in the rear assembly. This allowed the ring to slop around under load only. It sounded much like a teacher writing on a chalkboard and had a slight coinciding vibration on the floorboard. If I were you, I'd check all drive line components for failure and proper lube levels. I had to drain the rears to check the magnetic plug for metal, the magnets in the axle housing was doing a thorough job of catching the shavings from the failed bearings, so a simple finger dip in the oil didn't reveal any metal in the oil. Also make sure its not your clutch linkage or forks rattling around. Maybe they need grease or and end replaced.

I'd say does the problem go away if you push the clutch in but that takes the load off of everything. So you have to resort to checking everything properly in a static state (sitting still)