[bitcosmin]

Good evening gents!
Since a few days ago I m experiencing a very annoying and also strange sound with engine off. The sound is actually something like a whistle coming from the left side of the engine compartment, somewhere underneath the intake manifold/alternator area, after a few hours from turning off the engine and closing the vehicle. I must confess that I initially heard this whistle a few days ago and came back this evening after a 30 km trip in my crowded city. Is this sound coming from a vacuum valve or from the AC Compressor? No faults on any modules in ISTA-D 4.16.14, also the engine is working normally. Any ideas from a similar experiences would be maximum appreciated!
By the way, the vehicle in cause is a 2013 525d xDrive biturbo BMW .
This is the sound: https://www.youtube.com/watch?v=pUAvICCS3rU 
Thanks a lot!

[VAG]

Good evening gents!
Since a few days ago I m experiencing a very annoying and also strange sound with engine off. The sound is actually something like a whistle coming from the left side of the engine compartment, somewhere underneath the intake manifold/alternator area, after a few hours from turning off the engine and closing the vehicle. I must confess that I initially heard this whistle a few days ago and came back this evening after a 30 km trip in my crowded city. Is this sound coming from a vacuum valve or from the AC Compressor? No faults on any modules in ISTA-D 4.16.14, also the engine is working normally. Any ideas from a similar experiences would be maximum appreciated!
By the way, the vehicle in cause is a 2013 525d xDrive biturbo BMW .
This is the sound: https://www.youtube.com/watch?v=pUAvICCS3rU 
Thanks a lot!

Do you hear a scratching sound like metal on metal when you start your engine?And sometimes you hear it and sometime its not giving any sound,just the engine starts normal?

[bitcosmin]

No, the engine starts normal without any unusual sounds. I remember that I heard a small scratching sound a few weeks ago, coming from the engine compartment but it happened when I turned the engine off. It was a singular event. Thanks!

[VAG]

Hmm could also be a bad timing chain tensioner as that is quiet popular by the BMW special with the famous N47 engine and some of the 3.0 engines have problems with it.What is your engine code?And in mean time i would recommend you to go at a local mechanic who is a trusted guy that will not lie to you and let him check the chain tensioner.In time the sound will be more and more loud that would be the clear symptom of a bad chain tensioner.Hope i helped you have a nice day 

With best regards VAG

[larshutten]

Timing chain doesn’t look logical to me. He is complaining about a sound when engine is off usually timing chain stands still in that case?. I would check if there is an extra water pump and disconnect that temporarily. And search for vacuum valves/solenoids.

[karpiaavi]

vacuum leaking from broken actuator/solenoid, compressor bypass flap returning to rest position, throttle body jamming, air conditioning drying cooler core.. if it works fine don't fix it

[VAG]

Timing chain doesn’t look logical to me. He is complaining about a sound when engine is off usually timing chain stands still in that case?. I would check if there is an extra water pump and disconnect that temporarily. And search for vacuum valves/solenoids.

Yes correct but hi also heard a scratching noise like metal on metal,thats why i asked him to check,and also we can only think what it is until i clearly hear that sound.

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Vacuum hose can be one of the problems to,you need to check all the basics first than check for the other things in a particular order.

[bitcosmin]

vacuum leaking from broken actuator/solenoid, compressor bypass flap returning to rest position, throttle body jamming, air conditioning drying cooler core.. if it works fine don't fix it

The good part is that “the sound” appears rarely and everything works good now! NexT month I planned a visit to my BMW Workshop, so I m going to show them the footage so they Could come to a conclusion, which will be shared with you guys! Thanks again!