Well, today I replaced every single piece of vacuum pipe under the bonnet. Did it one piece at a time in case I forgot where the bits went. There was only one piece that was showing its age, and that is the one at the front that goes to to top of the engine on the left side, down the side and then across to the plastic pipe leading to the vacuum reservoir in the wing. Difficult to say if it had any leaks.
Started it up and left it idle for about 10 minutes before taking for a short drive, but the noise is still there. I did check that everything was secured including the heat shields down the sides, but I forgot to check the ones underneath this evening whilst doing another little job.
I also did another little video to check the vacuum pods and noticed that one of them seems a bit hesitant to move. I doubt it has anything to do with the noise I hear, but it looks like I may be attempting this job at some stage:
40V Intake manifold fix for stuck or sluggish flap pivots
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts
My DIY jobs -
Replaced alarm horn,
Replaced Coolant Temp sensor,
Updated RNS-D firmware,
Installed Reversing Camera and Digital TV,
Dashcam Installation,
Retrofitted Rear Blinds,
Auto-Dimming Rear View Mirror,
Chrome Boot Struts
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2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights
My DIY jobs -
Fan Jet Windscreen Washers,
Retrofitted Electric Side Blinds