Dbrook4005

I have a knocking noise coming from the engine area of my S-class. It only occurs occasionally after driving - not every time the car is taken out. The local Mercedes dealership has not been able to diagnose the problem. I am hoping that maybe someone in this forum has dealt with a similar issue and may know the cause. I have added a video giving an example of the noise.

Thank you

95Sinned420

Take a video of the hood open, in particular, the view of the Serpentine belt and the tensioner and pulleys.

carlosinseattle

Yes, definitely open the hood and remove the engine covers. See if you see anything. If I had to make a shadetree mechanic guess I'd say it's the clutch on your Ac unit. BUT..major caveat: That is what it would have been in the old school systems if you were low on refrigerant. The refrigerant also serves as a lubricant. So if the refrigerand was low, or the system hadn't been used in a long time, you would hear that little noise. I have no idea if that appolies to these cars or not, so I'm not even calling it a guess.

Dbrook4005

Thank you very much for your response. I took the car back to Mercedes when I heard the noise again. And asked if they had checked the items you mentioned. They finally fixed the problem by replacing the tensioner. I appreciate the help.

Debbie

AMG__POWER

Word of advice lol stay away from dealers find a good Indy Mercedes mechanic

Dbrook4005

Totally agree! The work was done under warranty so had to be dealer. Will find a good Mercedes mechanic to do future work.