Check the lash back and forth with the prop. The prop should only move a couple of degrees of arc before you should feel the gears loading up. If its more than that, you will have problems.
I've been bit by this bug because I had my engine overhauled as well as the gears. Even though everything was yellow tagged and certified, my combination of engine case and gears didn't fall within the lycoming specifications for gear lash. I even ran the engine on the test stand and it ran great. Problems was the excessive backlash and that "clicking". Had to tear it all apart and send the case out to be re-machined. As cases get overhauled, the mag gear post position gets closer to the centerline (which move the gear teeth tighter together). To offset this, the shop will weld up that hole and remachine it in a new position to have the correct gear engagement with the centerline gears (Cam and crank gears). I even bought new gears and it was still out to far. So back it went and they fixed the problem. Now I measure all the backlash in all my gears. That left mag gear is critical to to the timing of the engine and the camshaft operation. Too much play and it will eventually excessively wear things out, hence the tolerance needed in that position. Right mag gear just is a follower and doesn't time the engine. I would have someone check that out who knows what they are looking at just to be safe. If you have the inspection sheet that should notate that tolerance, then that would be nice to know someone checked that and that is not your problem.
