[Lancee]

I have just watched your videos (should have done the first time around!). The second video with the oil filler cap being removed shows identical symptoms to the issue which I had. My rear engine mount was leaking and after replacement the engine was much quieter.
The vacuum circuit is also involved with the turbo and possibly other functions, my cars performance also appears to have improved slightly, I believe the vacuum controls the turbo vanes.

Sorry to do this to death but (and I might be wrong), again there could be a leak elsewhere? The labour cost for your proposed work can't be cheap? How much would a thorough vacuum test cost, or buy the tool and do it yourself ( a useful tool to have anyway).

Try kinking the rubber vacuum pipe to block the circuit where it leaves the vacuum pump (top RH rear of engine) with the engine running and the oil filler cap removed and check the sound.

As a footnote, I am not an expert, I am only speaking from personal experience as a layman.

As a further note my local Volvo main dealer checked out the noise (for a fee) and said there was no problem although I felt sure there was. I identified the problem myself through the above methods. My engine mount was absolutely shot with a big split in the rubber.