I have an OM617 that has developed an odd kinda metallic clank at certain RPMs. I’ve looked but haven’t been able to find anything g online like what I’m hearing. Runs fine otherwise just at about quarter throttle it randomly clanks. Valve hitting the piston? Injector? I used a stethoscope and narrowed it down to cylinder #2, definitely top end of engine.

 

Dribbling injector. Get them all physically cleaned and recalibrated. Don't waste time on "mechanic in a can" chemicals.