Thumping noise on slow turns
Thread Starter
Newbie
Joined: Jun 2024
Posts: 4
Likes: 0
C300
Thumping noise on slow turns
2011 C300 4Matic Sport 110k miles
After coming back from a 2 week Christmas break, we came back to find a sudden mysterious thumping noise on slow turns right or left. No previous issues before.
No check engine or dashlights.
At first we thought this was a CV axle issue because of torn boots so they were replaced.
Nope, noise is still there.
Independent euro mechanic suggested a bad transfer case.
Well, my transmission guy pulled it out and transfer case bearings looked great. No wear.
Another but possibly other related issue is we have rpm flutter when we try to accelerate and a subtle driveline vibration. Spark plugs and coils were replaced. No dice.
We are now looking at possibly a bad front or rear differential.
Here are videos of the RPM issue
https://youtu.be/kR_kQFmCQY8?si=OexJw4yxCWuLBwY6
Noise on turn (better heard on headphones or speakers with good bass response)
https://youtu.be/YmwbikkgtE4?si=_xyO4pFfF2way2QQ
What does the hive mind think?
After coming back from a 2 week Christmas break, we came back to find a sudden mysterious thumping noise on slow turns right or left. No previous issues before.
No check engine or dashlights.
At first we thought this was a CV axle issue because of torn boots so they were replaced.
Nope, noise is still there.
Independent euro mechanic suggested a bad transfer case.
Well, my transmission guy pulled it out and transfer case bearings looked great. No wear.
Another but possibly other related issue is we have rpm flutter when we try to accelerate and a subtle driveline vibration. Spark plugs and coils were replaced. No dice.
We are now looking at possibly a bad front or rear differential.
Here are videos of the RPM issue
https://youtu.be/kR_kQFmCQY8?si=OexJw4yxCWuLBwY6
Noise on turn (better heard on headphones or speakers with good bass response)
https://youtu.be/YmwbikkgtE4?si=_xyO4pFfF2way2QQ
What does the hive mind think?
Last edited by aiforce1; Apr 6, 2026 at 09:36 AM.
Thread Starter
Newbie
Joined: Jun 2024
Posts: 4
Likes: 0
C300
Transmission flush was performed about a year ago but when my transmission guy checked it looked bad.
We are looking at the front differential now. We’ll be checking fluids again.
Does a bad differential cause transmission RPM issues too? Can they be related?
Last edited by aiforce1; Apr 6, 2026 at 09:42 AM.
MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,153
Likes: 1,767
From: Colorado
G550
About the 110K miles and I believe front differential fluid was changed when we changed the front CV axles.
Transmission flush was performed about a year ago but when my transmission guy checked it looked bad.
We are looking at the front differential now. We’ll be checking fluids again.
Does a bad differential cause transmission RPM issues too? Can they be related?
Transmission flush was performed about a year ago but when my transmission guy checked it looked bad.
We are looking at the front differential now. We’ll be checking fluids again.
Does a bad differential cause transmission RPM issues too? Can they be related?
Thread Starter
Newbie
Joined: Jun 2024
Posts: 4
Likes: 0
C300
i’ll keep everyone posted
Thread Starter
Newbie
Joined: Jun 2024
Posts: 4
Likes: 0
C300
Independent mechanic who diagnosed it quoted $2500 for parts and labor.
Don't know what to do now.
