Tommyhawk

Hello - I have a (new to me) 2006 CLK55 AMG Cabriolet with a clicking/ticking noise I need some help diagnosing. I am an experienced mechanic with over 30 year of working on German cars, but this one has me stumped. I have searched the forums extensively and I haven't found anything that matches the noise / symptoms.

2006 CLK55 AMG Cab, 90k miles

The noise sounds like a very light "lifter noise" or possibly a fuel injector tick noise - very light and precise, only audible in the cabin with ventilation and radio off. - the engine sounds "normal" with the hood open and listening from outside the car. It becomes more noticeable after the car has warmed up.
-- It changes frequency with engine rpm, not driveshaft speed. (car coasting in neutral at 10 mph, rev engine up, it follows engine speed)
-- Most noticeable under load and in the lower gears - once cruising at 60 mph it seems to disappear, even under moderate load.
-- The noise will come and go when hitting bumps or road undulations, or change slightly if weaving left to right, - engine mounts / tranny mounts ?????
-- It is definitely NOT a lifter. No lifter noise coming from the engine using a mechanics stethoscope.

Something related to the engine / trans that when it moves slightly under load it is rubbing something ??

Overall the engine seems fine, pulls hard, doesn't smoke, etc. Seems healthy. Trans seems healthy, no issues with shifts, etc. I will check the parking brake cable to see if it is rubbing on the driveshaft, but I doubt that is it - this noise is so precise and mechanical. No engine codes. Seems to run fine.
I'm stumped - there is no way the car came from the factory with this noise - any help is appreciated. FYI I had a SLK32 with the similar M112 engine (V6 version of the M113 V8) and it never made this noise.

C280 Sport

Next time I drive my CLK55 I will have to listen for it. I cannot say I have ever had a tick from the CLK55 engine. I know lifters ticking were a thing on many W212’s but never W209 AMG.

What about rockers? Cams?

Tommyhawk

It's not in the valve train, it has to be the engine rocking and touching something slightly at the back, or maybe causing something to bind slightly between the engine and transmission.

ambit

Engine mounts? Pop the hood, put it in D and watch if the engine shakes when you hit the gas a little.

Tommyhawk

Appreciate the reply - yes - I'm thinking engine mounts or rear transmission mount is allowing the engine/ exhaust / trans to move enough to rub up against something and create the noise.

C280 Sport

Any chance you can post a video of the engine running? I know sometimes it can be hard to tell from the camera but it won’t hurt to try

Tommyhawk

I found it. I was able to zero in on it using a mechanics stethoscope from under the car. Turned out to be a loose spark plug on the driver's side back cylinder. There may have been some spark plug wires that weren't routed correctly either. After removing the wires, tightening the spark plugs, and reinstalling the wires in the correct orientation it runs like new, no noises and sooooooo smooth. The PO had the spark plugs changed just before selling it......
Thanks to everyone for their responses!