Popping noise from rearend
 

okay. Ive had this car to the dealership so many times and, of course, they say they cant recreate the noise. so I am putting this out there for you guys. Maybe someone will tell me what the heck that thunking noise is. What happens is when the car has been sitting for over an hour or over night in my garage, i will open the door and I will hear a loud thunk coming from the rear of the car. it only does it once and the car will have to sit for another hour or so to reproduce the noise. but it its pretty loud. please see the videos I have attached. In the video, youll hear the door open, and a thunk right after. Its very strange... The car is not turned on. it is unlocked (as its in my garage) and I when i open the door and THUNK! every morning i go to work and every night i leave work. Its not the trunk lid, since it does this with the trunk open or closed. its not the fuel door as that makes a different noise. Im at my wits end... please if someone could tell me they have the same issue and how to remedy it i would really appreciate it. :smash::smash::smash:

Do you have airmatic? My car with airmatic starts making noise when I open the door as the compressor (located behind trunk panel on driver side) kicks in, but it doesn't sound like that at least in my car. Maybe you can locate the source better if you leave the trunk open during the hour or so needed to recreate it. Then have someone open the door while you stick your head in the trunk. After a few attempts (and several hours) you might be to locate it more exactly.

I don't have airmatic. I did listen to it when the trunk was open. It was coming from where the gas tank is. Thats why i think it has something to do with the gas tank or fuel pump.

I have the exact same issue 2014 E350 Sport CPO. I just bought the car with 18k miles. It has to sit for extended period of time (like overnight). Open any door then THUNK! It's loud sometimes and not as loud other times. Comes from rear of car.

maybe a trunk closing mechanism?

Nope it's not the trunk mechanism... it's driving me crazy....

Here's what I would do in that case.

Leave the door open, but find a way to keep the switch pressed, so the car thinks it's closed. Then try to replicate the noise by releasing the switch. That way you'll confirm that it's caused by the car itself and not by the physical disturbance when you open the door.

You can then try and pull the fuses for any equipment in the trunk area, start putting them back in one by one and repeating the test.

Please note that this is just food for thought with your best interest in mind. The 212 is so much more electronically complicated than my trusty old 208 :)

Threads a bit old, but I had the same issue on a 14 E350 and the dealer replaced the gas door lock solenoid for the fuel door under warranty. The part number is 204 820 53 97 fuel door lock actuator motor. So far no issues the past week.

Spoke too soon. The problem happened again this morning. But it's more of a groan sound now. It happens after the car has been sitting for a few hours and pressing the unlock button, even if the car is already unlocked. I'm wondering if it is a module that controls the central door locking system. I will take it in again when I have the chance.

Thanl you for your time keeping us updated