Most common issue would be the oiling tubes between the exhaust lifters to the intake lifters. The end plug, be it metal or plastic tends to fall out. This usually leads to a dominant ticking noise heard on the top end but mainly when the engine is hot.

I might suspect the check valve that is inserted into the oil filter housing, it may not be seating properly. The check valve is designed to maintain residual oil pressure in the chain tensioner and the lifter oiling circuits. I believe MB modified the valve to correct an intermittent seating issue.

Good luck