Got an S430 (not mine) with an engine tick at idle, sounds like it's on the left side (cylinder bank 5-8). You can hear it as you rev up the engine a little bit (it goes faster as the engine does), but it goes away. It's a bit louder when the engine's warmed up. It's louder than either of my S430's or the project 2000 S500. It's most noticeable when you pull up next to another car or a wall, or if you're standing outside the engine bay. You don't really hear it if you're inside the car with the windows rolled up.
The engine has plenty of power, seems to pull just fine, doesn't blow smoke, no drivetrain codes, no misfires, transmission not slipping, etc. Just that louder-than-I'm-used-to tick. Haven't taken the valve covers off yet, but like most W220's now, it's about due, and the owner's cool with that.
Been searching the BenzWorld forums for "engine tick m113", and nothing. Searching Google shows me lots of information for the M119 engine and the oil guides, but not quite as much for the M113 (does it even have these M119-style oil guides?). Some folks suggested either valve lifters or the EGR valve, but according to various posts out there (including BenzWorld), stuck valve guides happen when the engine's cold, and that goes away as the engine warms up.
If anything, it's almost the opposite, i. e. it's a a little bit quieter (not much) at cold-start and then gets to full loudness as the engine warms up.
IIRC, Dave made a suggestion as to what to look at. It was something in the oil pan, I think. I'm having trouble finding that post.
Can y'all be of some assistance?