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Discussion Starter · #1 ·
Hello friends,
I'm encountering really weird sound on my 2012 facelift A5. It actually happens only, when engine is cold (after startup). I've been to 2 workshops already, but they did not find the problem - since it happens only under certain circumstances, it's hard to diagnose.

It happens if following conditions are met:
  • Engine has to be cold
  • Engine speed has to be in range 1000-1800 RPM (approx.)
  • Engine needs to be under slight load (does not happen with clutch pressed/neutral and also does not happen with heavy load)
The sound itself is hard to describe - it’s low tone - humming/grinding sound. I made a quick audio of it (recorded about 2 meters from the car). It was recorded right after the cold start. I was slowly driving off from standstill to slight slope.

Link (headphones recommended): https://soundcloud.com/kamil-ture-ek%2F20-tfsi-noise
The sound is hard to pinpoint. It's audible from the whole engine compartment (maybe a little bit more audible from the turbo area), and it definitely comes from intake also (when i get closer to intake port, it's really loud).

Important thing to note is, the car is running perfect. It does not consume practically any oil and it drives really well. VCDS does not show any faults, workshop also tested the compression and it's around 11,5 Bar (+- 0,2) on all of the cylinders. So engine seems to be in really good health (apart from the weird sound :)).

I'll be grateful for any ideas/thoughts what might be the cause, or how could I proceed with diagnosing. I'm really desperate, because as I wrote: nobody wants to waste time with such sporadic fault I suppose.

Thank you.

Kamil
 

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Kamil old fruit, how many miles/kms on the car and is she consuming any oil??? Auto or manual???
 

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Discussion Starter · #3 ·
Hello Simon, the car has done 170k Km so far. I'm changing oil every 15k and i'm not adding any oil in between (so I assume the oil consumption is minimal). And she's manual... I noticed only one thing - when i remove the oil cap (when engine is running), there is a small vacuum and engine runs rough. When I do it on my 2018 Superb (with 2.0 TDI EA288), there's no vacuum. It may be normal - don't know.
 

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This is a strange one indeed. I have never had that engine so I am sure some of our experts will be along to help soon.
 

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The 2.0 TFSI gasoline engine is designed to have vacuum throughout the top end. So it's normal for your car to run rough when you take off the oil cap and break the vacuum.

As for your noise, if it's coming from the intake side, I'd check for leaks/loose bolts. It could just be a natural resonance that's vibrating the intake airbox. Check for loose bolts or wornout there are rubber bushings that mount the intake box to the car body.
 
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