Beyond head bolts, the M156 is watched for camshaft/lobe wear and ticking lifters or cam adjusters, with oil-change history cited as the key defense. Cold-start ticking that clears once driving is reported as common and not necessarily alarming, but worn cam adjuster plates are a real cost during any top-end work.
M156 valvetrain: cam-lobe wear, lifter tick, cam-adjuster rattle
Mercedes-Benz E55/E63 AMG (W211) · mechanical