Assistance with engine and gearbox noise

[MotoGravity]

Greetings to everybody,



Could someone please have a listen to this engine sounds and tell me what it is? I'm having trouble figuring out where it's coming from.

[MotoGravity]

For context, consider the following:
- 64 plate Mercedes C Class 250. Section 205


64,500 miles.


This problem typically manifests in manual transmissions when the vehicle is in high gear (5th) and the engine speed is low, such as 2k \.


On film, the noise appears when gear changes from fourth to fifth, which is when the automatic gearbox typically shifts from fourth to fifth and the RPM lowers.


- this noise only occurs when you're pulling (i.e., going uphill or accelerating); as you let off the gas, the noise stops.


The noise only happens at low RPM 2k < and high gear 5 >, therefore it doesn't happen in sports or sports plus mode when the RPM is greater before shifting gears.


- coasting prevents this from happening.


— not even when the engine is revved all the way to red line in neutral.



The noise finally became audible a few weeks following a comprehensive service at a Mercedes SPECIALIST facility (not a dealership) in my area, during which they changed the gearbox oil and filter.



As far as we know, this is the first service of its type based on age and mileage.



The garage I spoke with over the phone claimed that the oil change was just usual and that they use a computer and software to perform it, along with real parts and oil, so I should bring it back on Friday so they can check their work.



Since I witnessed the delivery of the items when I dropped off the vehicle for servicing, I am certain that they used Mercedes oil and parts.



Anyone have a clue as to what may be making that noise? I'd like not walk in on Friday and accuse them of botched service. Perhaps a loose panel or component, or an inadequate amount of gearbox oil?



In case you can't make out the sound in the video, it sounds like a motor, vibrating, or clicking noise. This effect is temporary when the engine speed is low in high gear; it disappears as the engine speed increases or when the paddle is used to manually shift back into fourth gear.



I would much appreciate any assistance.

[MDMH757]

it's hard to tell, and you can end up following unicorns in circles before you figure out what's making all the noise. On the other hand, if they've taken off any heat shields or coverings, it might be a vibrating unicorn. Is the sound emanating from the vehicle's interior or outside, the front or the rear? Though I've never heard anything similar, I think it might be worthwhile to investigate more.

[MotoGravity]

I appreciate your response.

What a strange sound! I hope it doesn't cause any costly problems. I'm crossing my fingers that it's just a heat shield or a loose panel.


It sounds like the engine bay or somewhere nearby is where the noise is coming from.

Would this be the same if they haven't oiled the gearbox enough?

[MDMH757]

Hopefully it's not something major, but my S204's plastic engine covers and pipes wobble like crazy. It's a poor design; I would wreck the vehicles if I could.
Mine is a lot quieter once I take off the engine covers.