I have an e550 coupe with the m273 engine and recnetly when i've started it I get a high pitched whistle sort of noise. I think it may be vacuum related and seems to only be doing it on very hot days. I sprayed some brake cleaner at the front of the intake manifold and the noise went away also the engine strated to shake a bit. Does this mean my intake manifold itself is bad or some hoses around it? I tried to look at the hoses on the front but it is pretty difficult to see without removing the secondary air pump. I did notice a bit of wear on the outside of one of the hoses going to the intake but no noticeable cracks or holes. It looked more like the part was rubbing up against a metal component that got very hot. I also had a shop smoke test it but he ran it through the oil filler and we didn't see any leaks. Is there a better place to run the smoke test through? There are no lights on the dash btw and when the shop scanned there were not even any vacuum related codes or lean codes.

 

A faulty EVAP system vacuum leak would bring up a code guaranteed and your good car has none.

Does the whistling stops when you remove the oil filler caps off the valve cover? It may be time for a PC refresh.

Any service done recently that may have disturbed hoses???

 

Is your airbox sealed tight? I noticed a whistle after changing air filters and noticed one of the screws that hold the box together was loose and causing one side of the airbox to have a virtually invisible gap until the motor was pulling in air.

 

It never stops until I turn the car off... but when I take the oil cap off very small amounts of oil will spray out. I thought this had something to do with vacuum leakage. Sorry if this is a stupid question but what is a pc refresh? I had the alternator changed recently and i'm sure they had to remove the fan and probably some other components I think the noise may have began around the same time but I am not completely sure. Also the ac clutch burned out recently but that part was changed and it works good again.

 

I'll check that out but I think i've taken the whole airbox fixture off and it still made this noise I don't think it is coming from that area.

 

I think you're about to solve a couple good problems for your precious car.

I think both your alternator and AC clutch got wasted by the oil leaking out of the valve covers! How much was that?

These leaks were caused by the defective PCV circuit, hardly a system bit a German money maker for sure. The failed PCV was putting your crankcase under pressure and breathing oil out of everywhere possible... over your alternator and over the A/C compressor...
- Is that sad for owners or is that good business ???

In plain english that means you may get concerned with MB "oil in harness" infamous topic. It can get expensive when oil contaminates the whole engine harness towards the ECU box. That is called opportunities

Act quickly to improve your odds:

1. - check your VVT solenoid connectors
2. - check your camshaft sensor connectors
3. - check ECU connector
4. - replace PCV and plastic lines to intake (*)
5. - Find a better shop to work on your dime.

* : this is what I called "PCV Refresh". The plastic pipe lines get brital from high heat. The PCV tiny rubber seal got disappeared into your intake track.

All of the above is "casual DIY" fare around this forum. Remember, these good parts are cheap at Pelican Parts...

 

Thank you I’m not sure on all these pieces you mentioned but I’m sure google will help me. But the source of my issue is the brittle vacuum hoses going to the intake manifold? These are located behind the secondary air pump correct? That is where I hear the noise predominantly and that is the area I sprayed brake cleaner to temporarily stop the noise. I have been noticing some oil under the hood basically right above the engine cap and I had thought it was because my previous cap had a crack in it. I replaced the cap and still notice this. So basically the vacuum leak is causing pressure in the crank case and oil to shoot out through the cap? I wonder how the mechanics I had taken the car to were unable to come to this conclusion.

 

... yeah, me too

​​​​​​Dentists talk about tooth decay, never about bed time candies or corn syrup sodas....

The failed PCV is an excellent cash-cow that delivers gravy throughout the world

 

Well put lol. Thanks for your help on this.