Probably one or more stuck lifters, but a MB V8 likely could use a chain at 150k. They have really long serpentine timing chains, yes? More links on the chain, the more elongation will occur, am I right? The more elongation, the harder the tensioner works to keep the chain taut, etc. etc. If the engine was not abused and had frequent oil changes I would wait until 200k to change the chain. That's a major job on a V8.

Start using some good synthetic oil in it. After a while it sort of makes the noise go away.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)