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This is an '05 A3 with a 2.0 TDI BKD engine, about 120k miles on it. The sound starts when I move the key to the ON position, without starting the engine. But even with the engine on, it's still there, and it stops about 10-20 seconds after I remove the key. What could cause this? Here's a video of the sound

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    I'm thinking this is probably the EGR valve fluttering ... I know there is a valve which Audi's have had an issue with which do exactly this ... I wrote an article on it ... when I get home I'll look it up ... NP80? "Something" 80 valve. Not sure if the TDI has the same valve as the gas engine does, though ... I'll see if I can find it when I get home. Jun 16, 2016 at 18:06
  • Can you narrow down where the sound is coming from? Something that loud I'd imagine you could put your hand on and feel for what's buzzing.
    – Ben
    Jun 16, 2016 at 21:08
  • Okay, I was thinking of the N80 EVAP purge valve. This applies to Audis with the 2.0TFSi engine, so I doubt it is your issue with the TDI. Jun 16, 2016 at 21:46
  • Could be a fuel pump - if you get outside the car with the ignition on, you should be able to roughly hear where the noise is coming from.
    – PeteCon
    Jun 17, 2016 at 1:19
  • Thank you for your answers guys. I tried to pin down the source of the sound and I think it's coming somewhere from around the EGR valve as Paulster2 said. Picture, the highlighted part is where I hear it the most, OEM part no. 038128063G, which google tells me is called throttle body, but I can hear it from the EGR valve next to it too (I used the screwdriver as stethoscope method). This morning however the sound was much quieter, you can barely hear it with the hood down. It was a whole different story yesterday. Video today
    – Steve
    Jun 17, 2016 at 12:22

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That's the anti-shudder valve (ASV), D, in the image below (from an article on how to delete the EGR/ASV – not a good idea on a diesel as the ASV provides some measure of protection against a runaway) it should be fixed open (and I would think quiet) when the car is running. This video "Noise of a Anti Shudder Valve / Inlet Manifold Flap ready to blow" is similar and suggests impending doom (or at least failure of the valve). If the valve fails open, you probably wouldn't notice anything by the quiet (barring a runaway), but if it failed closed then you wouldn't be able to start the engine (or at the very least power would be severely limited).

Location of anti-shudder valve (D)

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