When my wagon is cold, as soon as I drive out of the driveway, I hear a 60Hz low rumble. It’s smooth in sound, as if someone is playing a low 60 or 80hz sine wave through the subwoofer. Once the car is warmed up, no more rumble. It is not speed nor RPM dependent. I hear it more when I’m driving slow, under 10mph and turning. But it’s there even when I coast in neutral down the hill we live on. I can rev the engine while it’s happening and the sound does not change.

i tried to record it but my iPhone doesn’t capture something that low.

any idea what that could be? Is there some part of the engine that runs only when the engine is cold? My E46 M3 has a secondary air pump that runs for a couple min when cold.

so odd that it goes away once the wagon is warm. The car has 130k miles on it fyi.

 

Now assuming you are accurate on the 60 to 80hz sound you are hearing, if we convert that to rotational speed, that is :
60hz x 60 seconds in 1 minute = 3,600 RPM
This is not idle speed but can be engine exhaust pulses.

I do not know what engine is yours because I do not see a W212 and its model year in your signature, but I assume it is a 6 or 8 cylinders.
Cold idle at 30C / 88F if M276.8 3.0 Turbo is 1,300 RPM and slowly brought down to eventually 650 RPM. I believe this strategy would be the same for most MB engines.

To my understanding this 60 - 80hz is there at cold start and gone when engine has warmed up...correct ?
At cold idle RPM and a 6 or 8 cylinders, there will be 6 or 8 exhaust pulses per 1/2 of engine CRANKSHAFT idling speed or we can call it CAMSHAFT idling speed.
4 stroke engine need 2 CRANKSHAFT revolution to fire all cylinders.




I believe what you are hearing has to do with exhaust system hangars 4 of them and the small vibration damper. Renew those 4 super cheap rubber exhaust hangars.
My M276.820 3.0T has one small vibration damper at the middle silencer , the one after the CAT.

Example from a Ford truck



If your car is already at 130K miles and is on original engine and tranny mounts, those 3 have to be renewed too.
Engine and tranny mounts dictate overall alignment of your exhaust system and the tranny to differential alignment, so it is a BIG thing.
People assumed engine mounts only absorb engine vibrations, they do not realize the required like maximum <2 degrees tolerance of the alignment
of tranny output to differential can go bad from collapsed engine mounts.

Take a peek at your 2 engine mounts, 1 of tranny mount, 4 of exhaust rubber hangars and if that small exhaust vibration damper is there or not ?

As to why when engine is hot and the 60-80hz gone, I suspect it is from the exhaust system expansion.
Watch below and see the green arrow showing exhaust system expansion from cold engine to warm.


Good luck

 

Agree, engine or exhaust mounts need replaced.

 

+1. Just changed our engine/transmission mounts (at 140k miles), and the cold 'rumble' went away completely.

 

@S-Prihadi holy cow!! Thanks for that very thorough explanation! Mine is a w212 E350.

and yes, I’m an audio engineer and the rumble lives in the 60-80Hz range.

this makes sense about the exhaust resonating. I will check the mounts today to see if I can see any obvious wear.

I think I can see the motor mounts from the top of the engine. I’ll look at them for any obvious wear as well. Not sure I know where the transmission mounts are but I’ll look on YouTube for that.

and thanks for the other two answers. Such a helpful forum!

 

You likely can't 'see' worn engine mounts from the top side.

When they are worn, they collapse, and allow the engine to rest on a rubber 'tab' which then rests directly on the bottom part of the mount - which is hard-bolted to the chassis. Thus, any engine vibration is transmitted via the hard rubber tab from engine to chassis.
You can check by putting the car in FWD, opening the hood, and having someone rev the engine (FOOT ON BRAKES!!!! Obviously). If the driver's side of the engine rises significantly during revving in FWD, then the mounts are worn. S-Prihadi has a detailed thread on this topic: https://mbworld.org/forums/e-class-w...omponents.html

 

the transmission mount has more of an affect on NVH, is much easier and breaks way earlier than the engine mounts on the 212's. My mounts were OK at 120k, all the fluid still in them. My trans mount at that mileage was missing