Strange sound from under the bonnet when ignition is on

[Alex5555]

Hello,
I've checked the forum but because my knowledge of the car is not great and there are a lot of simptoms I can't understand if it is normal or not. Basically when I drive and stop so that my Start/Stop system stop the engine I can hear random repeated sound from engine like something moving inside or drill perforator works. It makes that noise several times then stops. I can hear that noise once sometimes when in the morning I switch on ignition. I suspect it is fuel pump. Is it normal to be so loud that I hear it from inside the car? My main worry is that for the first time I had full service done not at VW dealer and they may not purge system using computer but just started the car.
Golf 6, TDI 1.6 Bluemotion, 2011

[Alex5555]

https://youtu.be/gmQbaZQHe-8
I recorded sound, sorry it was very dark. The sound I mean is at 6sec-8sec on the video. So on the video I just switched off engine but when it is stopped by Start/Stop then it may happen several times as a pair of two sounds like something moves and then returns.

[froudeg]

https://youtu.be/gmQbaZQHe-8
I recorded sound, sorry it was very dark. The sound I mean is at 6sec-8sec on the video. So on the video I just switched off engine but when it is stopped by Start/Stop then it may happen several times as a pair of two sounds like something moves and then returns.

That to me sounds like the antishudder flap (sometimes incorrectly called the throttle body, which a TDI does not have).
This flap closes when you shut the engine off - closing the intake off and preventing the engine from shuddering when it shuts down.
It also has a secondary safety purpose - it prevents a diesel runaway happening whereby a faulty engine/turbo can eat and run off its own engine oil - using it as fuel. The only way to stop this is to shut off the air supply, which is done via this flap when you turn the engine off.

For some reason it sounds like its opening and closing again - it could be faulty or need cleaning. It should just close when you shut the engine off and then open...but it seems to be cycling.
It's a separate unit that can be replaced (its not internal to the engine) and will be near the intake manifold.

Doubt its the HP fuel pump - its mechanically driven so with engine off it will be doing nothing. The LP fuel pump is under the back seat.
Nothing else mechanical runs when the engine is off but that control flap...the high pitch whine you can hear will be the PWM control of that flap.

Best get the car scanned for codes first to see if it has come up with any errors.

[Alex5555]

Thank you for the answer. I've scanned car for codes and it doesn't have any related, only rear bulb and radio issues. As for the flap, do I have to worry about it and take it to the garage or keep driving? Will it lead to a more seriouse problem such as EGR failure? Or can it be cleaned adding some special cleaning additives to the tank? I have beed using only Shell regular diesel for the last two years.

[froudeg]

Thank you for the answer. I've scanned car for codes and it doesn't have any related, only rear bulb and radio issues. As for the flap, do I have to worry about it and take it to the garage or keep driving? Will it lead to a more seriouse problem such as EGR failure? Or can it be cleaned adding some special cleaning additives to the tank? I have beed using only Shell regular diesel for the last two years.

You don't have to worry about it - worse case it will stop working and will just be stuck open, the result of which is that when you turn the engine off it may occasionally shudder as it shuts down - but this doesn't cause any harm.
If it does fail completely it will put the engine management light on, so you will know. It will probably carry on being twitchy on shutdown for a while until it eventually fails.

It will have no effect on the EGR.
Cleaning additives will have no effect as it sits in just the air flow before the intake manifold.
Carry on using shell regular diesel - its good stuff and no need to go for vpower etc