fred.lum

New member here. I have a 2005 C230 Kompressor and have been trying to identify a strange noise being emitted from the engine. The car is an automatic and the noise only occurs when in drive or reverse at low idle. It goes away when in park. Seemingly, it's coming from the upper right side of the engine near the intake. After first noticing the sound, I had no choice but to drive home 120 miles and lucky the car got me home with no issues. Recently, I replaced the voltage regulator due to charging issues. Other than that the car is completely original factory parts. Can anybody recognize what this sound may be. Thanks in advance.

slammer111

Check the pulleys. Remove the serpentine belt and try spinning each one by hand.

Does the problem go away as soon as you start rolling? Are there any signs of slippage on the belt? (the surface on at least 1 side will look "polished" if the belt is slipping)

The one that is most famous for failing is the one-way alternator pulley, but that one is on the other side of the engine. However it is also the one that often causes a squeaking noise when idling in gear. The sound in the video isn't the exact same sound I remember, but hopefully it will point you in the right direction.

fred.lum

Thanks for the reply slammer. I too was also suspecting a pulley issue due to the issue only occurring at low idle. Going to pull the serpentine belt later today once I can find that damn torx socket. Will post later with my findings.

slammer111

The alternator pulley is differerent from all the other pulleys in the system in that it must freewheel in one direction and not in the other. The quick way to check (with the belt off) is to quickly spin and stop the pulley with a flick of the wrist. The internals of the alternator will provide more than enough mass to freewheel the pulley if it isn't seized.

There will be some resistance in the freewheeling direction, so don't expect something like a bicycle wheel. What you're looking for is whether or not the alternator is able to spin independently of the pulley.

I forget which direction the pulley is supposed to freewheel, so just try both. I'm pretty sure this is the cause of your squeak. This particular pulley is a wear item and needs to be replaced every few years, and the original version doesn't last too long before seizing up. Hopefully the newer updated ones last longer.

fred.lum

I just got the belt off and all pulleys are spinning freely. Regarding the alternator pulley, it is spinning freely in both directions. I stuck a screwdriver in the internals of the alternator and the pulley seizes up in both directions. Therefore, the pulley is not spinning independently from the alternator. Is it supposed to spin independently or does this indicate that the pulley is bad?

Found another youtube video and the noise this guy is experiencing is similar to the one I'm hearing. OP replied saying the supercharger was bad. Although, someone in the comments stated that the alternator pulley turned out to be the issue like you had suggested. Video link here:

slammer111

The alternator pulley has gone bad on you. The pulley should be able to turn freely in one direction while you have a screwdriver jammed into the alternator.

In the link I provided, there is a pulley replacement video where the guy is able to turn the inner spool (the part that screws onto the althernator shaft) of the new pulley with his tool. On mine I was able to turn it by hand. Once you play with a new one you will see what I'm talking about.

Lastly, be sure to order the correct one. There are 2 variants (different PNs) with different physical dimensions, depending on alternator model. I would call the dealer and provide a VIN to know which one you need.

Good luck.