Greetings,

My 2009 E550 has occasionally made a very quiet tapping sound at ~3k RPM when accelerating, I could never figure out what it was. Recently it has become much louder and metallic sounding, so it's clear to me I need to figure this one out. Luckily I can still drive the car while never going above ~2.5k RPM due to the mountains of torque M273 makes, haha.

Car has 101K miles, no CEL or codes, premium fuel only, well maintained with all fluids changed, engine, trans, and diff oil. The previous owner changed the transmission oil, though I am unsure if he also did the torque converter. The engine has no hesitation or power issues minus one instance a week ago when I was moderately accelerating up a hill and at ~3k RPM I heard the tick and the car shuddered a bit. That was a one off scenario. I can feel the transmission shift when cold, but when warm it's smooth as butter minus 2 - 3 where I can feel a mild shove occasionally. Not sure if this is related, but when and after I drive it hard I notice a bit of whining matching the RPM's of the engine, seemingly only after prolonged driving.

So I'm not sure if the metallic tick sound is coming from the engine or the transmission, though if I have to guess it's the engine. As for what the problem is, I really don't know, though I have heard cam adjusters can fail on these M272/3 engines and make a sound like this. Could it be spark plugs? Torque converter?

Edit: Beginning to think it's pre ignition or detonation, I'll be cleaning my air injection check valves tomorrow. Probably wont fix it but it's better than just throwing new parts at my engine. Anything else I can clean that would contribute to pre ignition?

 

Hello,
Thanks for the details, the m273 engines had the timing chain stretch/issues in general which could be the beginning for your case. But it might throw cel codes and timing codes which you don't have. It could be the lifters starting to wear out, this was common on the 272/273, it doesn't affect performance just the sound. The 722.9 trans are pretty stout and haven't had issues with them especially if you do the maintenance on it. Adjusters could be another or the magnet solenoids, they have had updated versions throughout the years, this would be the cheapest fix. Also, there is a purge value on the left lower under the left intake hose which can make a ticking noise when the car accelerates, you can take of the intake duct and listen to it, should be obvious if coming from there. If you have a stethoscope try listening to where its coming from, put the probe in different areas on the magnets, valve cover, etc... If you could also post a clip of the sound.
Hope this helps!

 

Thanks for the feedback. So I recorded some videos of the engine at idle and being revved, and a tick can be heard from the right side of the engine. The ping under acceleration sounds like it may be coming from the right side of the engine as well. Perhaps it is worn lifters, but why would they only be heard at 2-3K RPM when accelerating and potentially cause a shudder?

Here is idle:
Here is rev:

 

Any luck tracking down or fixing the noise you have? I changed the serpentine tensioner and the pulleys thinking it was these but it wasn't. So many things say engine mounts but I would expect the tapping when revving.
I'm chasing a tapping/ticking noise that only comes when accelerating, starts around 1800rpm. Free revving or even stalling up on the brake it doesn't make the noise. But moving forwards this tick/tap noise starts & if you stop moving the noise stops. But to be extra annoying it doesnt happen everytime I drive the car, rolling in neutral or when slowing down.
I'm thinking of using different brand of oil filter & slightly thicker oil. I am getting close to 260,00km.
Hasn't hurt performance or fuel consumption, it just sounds crap & I'd rather just hear the V8

 

It sounds like we're experiencing the same problem. Does your noise stop after some RPM or keep going until redline? I said 3k in the title but it's more like 2-3k RPM for me. I haven't figured it out, but its been a while since I last heard the noise, probably because I've been driving like a grandma lately . I've got ignition coils coming for rough idle, I doubt they are the source of the noise but I hope they fix it. Switching from 0w40 to 5w 40 had no effect on my noise. It seems like it could be anything but my best guess is something cam adjuster related. Do you happen to also have the infamous warm start knock? Where if you leave the car sitting for an hour or so to find it knocks for a few seconds when started? It's allegedly harmless but I wonder if these are related.

 

I don't have the start up cam adjuster knock/clatter, also came across this suggesting when searching. Even after a week of not being driven.
I replaced the chain adjuster also thinking maybe it was worn out but it was in pretty good shape.
My car is pretty loud so the exhaust roars over the tick/tap from around 2k rpm & I can't hear it, If I get in to 3rd while going slowly the noise also settings down quite a lot.

I've been running a 5w40 oil of the last few changes, it's pretty warm where I live in Aust for most of the year. I checked all my plugs and they all looks to be much the same. I have a slightly rough idle, but I think maybe this is early sign of engine mounts.

Last night I heard going along the drive way so I stopped, revved in neutral didn't hear it. Stalled up on the brake & didn't hear it. But moving forwads after a couple of meters I heard it again. It does sound like somethng is spinning to make the noise, not so much tapping

 

I managed to track down where my noise was coming from & it was the starter motor. Replaced it and noise gone! Was not what I thought it was going to be, but when I took it out and shock it there was a rattle. But great news as it was a cheap & easy fix. Was dreading the noise coming from inside the motor.