CLA45 SB 4matic have a “Bon” sound when coasting to almost standstill

[SK2]

I have a CLA45 SB (X117) that makes a 'Bon' sound in the rear when coasting to a stop.
It should be the sound of the rear differential. I've changed the differential oil and relearned but the sound persists. I tried replacing another differential , but had the same problem. Do you have the same question? ps: no error codes in diagnosis

 

[bembo449]

video or soundclip ?

 

[SK2]

There is sound at 38-39 seconds of the video; please ignore the dialogue in the video. : p

 

[Blobcat]

There is sound at 38-39 seconds of the video; please ignore the dialogue in the video. : p

Video has sound at 38-39 seconds; please ignore dialogue in the video