upi89

I already opened this thread on C205 thread but there are not a lot of owners on that part of the forum - not that many coupes I guess. Because C205 and W205 are not that much different I'm posting my problem here:
For the last 6 months my 2017 (bought new) coupe is making thumping sounds (coming from the back of the car) when taking off from standstill. The "thump" sounds like a spring releasing or something simillar and is driving me crazy. It appears right after car starts rolling but never befor I touch the gas. Been to the dealer several times but no fix.
Also noticed similar thump when crossing 50km/h ( 31mph) coming from the drivers footwell. It only happens once when I cross the 50km/h first time after car was resting for at least 30min. My W204 was making the same thump at crossing 50km/h but it was never thumping at taking off.
Has anyone got any ideas what this thumping could be?

upi89

Anyone?

Jan AMG

Rear subframe check?

upi89

Yes multiple times. It is also strange because I get thump sound at take off only after passing 50km/h (after inital thump described in the first post). I can take off 100 times before and no thump. Strange... I think it could be something with breaking system...

Jan AMG

I remember I had the same problem on my W210 and couldn't figure it out (swapped axles, diff, all subframe bushings, shocks, etc.). I have also replaced the whole drive shaft and took out the tq. converter and it didn't help.
How about that PET water bottle in the trunk? *Jokingly

upi89

Weird...
I also noticed this initial thump at 50km/h / 31mph can also be felt through the brake pedal so I think it could be the breaking system but don't know what to check.
At the dealer I got some BS about oil being cold and thick and it needs to warm up to go away...
Also found someone mentioning ESP initialization at 50km/h / 31mph ... I guess it could be because it happens every time but only the first time I pass 50.