On the D3 Aircon is permanently drive, not electric clutch like in older cars. It has variable valve which regulates cooling so it makes sense that it's still working for a little while after you press Econ button until the built up pressure dissipates

Yeah interesting, that makes sense.

How big a job am i looking at to replace the AC pump?

So i just had the air suspension compressor replaced yesterday as it was taking a good while to raise the car in the morning.

Noise is still there lol! Driving my nuts.

That's a real pain when you've gone to the hassle of replacing parts. Rereading the entire thread, did you ever pursue replacing the A/C compressor (not that I'm implying that that was the cause)? Just trying to eliminate possible options.

Is it possible to try and record the noise? I know it's not great, especially when the noise you want to record isn't that loud and the engine tends to drown most of it out. There's also the issue that unless it's a very unusual sound, most people won't pick up on it.

It's a bit of a long shot and hard to say without experiencing symptoms in person. Could it be climate control fan touching the casing?

I had kind of similar experience on Q7 after replacing climate control fan. Starting up, fan running at slow speed no noise; not sure if there was noise when driving and speed pushing more air through fan and making it spin faster and touch casing but me just not hearing because of other noises when driving. Or maybe it was braking forces shifting fan wheel just a bit so that it touches casing when braking but I could hear noise coming to standstill and it would stop after couple of seconds of being stationary. Taking it apart and reassembling making sure everything was seated correctly made it go away.

Sorry just noticed replies,

So I havent pursued the A/C compressor change yet, its one of the few things i havnt touched however the AC works fine whether the noise is happening or not. For example when i start the car first off, the noise isnt there as it only tends to show when the car is moving at low speed. But i can sit stationary and AC works perfectly.

Re the climate fans possibly touching a casing, it could be that but the noise has a very definate start and stop to it that doesnt fit in my mind with a fan gently nudging up against a case.

Just to reitterate, the times i can hear it is when the car is moving at slow speed. It stops abruptly when i bring the car to a stop every time. (this makes it hard to locate as i cant open bonnet to find when stationary)
It then starts sometimes when i start moving, maybe 5-10mph+ but not always, maybe 25-50% of the time when pulling away.
I cant tell if its happening at high speeds.
Its usually worse when the car is cold but not always.
It happens no matter if i have the A/C on Eco setting.
It happens no matter if i turn the entire climate control on/off.
Its coming from the front left hand side of engine bay from my drivers perspective.
It sounds like a pump that is trying to pump something but the reservoir is dry, that kind of groany grumbling noise you get when a pump isnt pumping liquid anymore.

I will try and get a recording of it...

Thanks

Something to consider if you have access to one. Do you know anyone who has a car lift that could help you for half an hour or so. If so, raise it enough to get the wheels off the ground, have someone 'drive' it at the 5-10mph speed you mention whilst you listen in and around the engine bay, as you are familiar with the sound.

Go through the various examples of when it's likely to happen, and see if you can pinpoint it any better. You should stand a better chance, as you would be eliminating wind and tyre noise from your surroundings. You also have the opportunity of being able to move around the car both left and right, and from above and below.

Checked the PAS fluid reservoir?

Ok so i have checked the reservoir, its full yet the power steering has been a little on the heavy side for a good while now and hadnt thought much of it until now.

Is there perhaps a filter blocked or perhaps power steering pump that may be on the way out? Where is that located?

Check the following PDF from page 284:

39-Service Manual Running gear front-wheel drive and four-wheel drive.pdf