Hello everyone- I have the M276/W166 2012 ML350 4Matic. I am getting a whistling noise on cold starts (always used to before as well) near the serpentine belt/pulley under the hood. I changed the 6 intake manifold gaskets and crankcase vent valve since I got the P2279 code for vacuum leak. This noise doesn’t come in warm season. Moreover it goes away after a few minutes (always used to go away after a few minutes and repeating the same even now after the replacement was done) but there is no error code coming up now. I have seen various other videos if you can search on YouTube as well where some suggested the breather valve/crankcase might be the issue but I got to hear again this morning even after the replacement. I have just given up. BTW I changed the serpentine belt as well a few months back but that did not help. Have you ever heard anything of that sort? May be I can share the video to you?

Video link here -

 

Did you also change all the idler and tension pulleys that the serpentine belt touches?

 

No, the mechanic did not recommend to change any idler and tension pulleys. Can you please check the video I have edited and pasted on my earlier question?

 

Remove the serpentine belt and spin each thing it touches (idlers, tension pulleys, alternator, etc.) until you find the offending part(s). Sure sounds like an idler bearing to me.

Then: fire your mechanic. Change all of the idlers and the tension pulley too. You do NOT want a seized bearing and shredded serpentine belt leaving you unnecessarily stranded.

 

I have changed the serpentine belt barely few months back. This noise does not come in warm weather or summers but only in the winter and that too on the first start of the day. Do you know what the labor effort hours needed and parts ID please?
I have burn it my pocket enough already now

 

No need for a new belt, but in my experience the symptoms you describe point to a bearing that is going bad. Easy to diagnose per post #4, then go from there. If a pulley is noisy enough to hear when you spin it, it is too noisy.

 

Pulley, tensioner and belt. Replace them all based on good practice.

This is an old car and the aforementioned parts don't last forever. Time to replace them.