Octavia - Knocking noise when cold and stationary

Hi all,

I have an Octavia 57 plate, Mark 2 Ambiente, 2.0 TDI, DSG Auto.

When I start her from cold (less than 10 degrees Celsius approx.) and she is sitting stationary, either just before I drive away or when sitting at junctions/in traffic, there is a knocking/rattling noise coming from the offside engine bay, low down.

When I accelerate, even a tiny bit, the noise stops. It also doesn't happen when I let go of the accelerator but am still travelling at more than about 5mph. The noise also stops after a few minutes, once the engine warms up a little, and it doesn't happen at all on warm days.

I am wondering what it could be? It's been very difficult to narrow down by getting out and listening around the engine bay, as the noise is very audible inside the vehicle but engine noise with the bonnet open makes it impossible to hear it very well from outside.

Due to the relationship between the knocking noise and pressing the accelerator, I know it isn't the fans/loose plastic trim/etc. This has all been checked/smacked/held to be sure.

I assume, with my little knowledge, that it could be one of the items on the side of the engine block, such as the water pump or a tensioner. Does this sound possible?

Any ideas?

Thank you.

I would start the car cold with the bonnet open and watch the tensioners as on another car I had the spring had gone sound similar

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When it is hot you will have the AC on so turn ECON off and see if the noise goes, the AC pump used is a known rattler.

If not the ac pulley, check your auxy belt is not flapping about at tickover and the tensioner knocking. I had a flapping belt caused by the alternator pulley sprag clutch being seized