Strange sound, oil cap pulling off

Z4, 2007 3,0 si, almost 100k km, Mobil 1 0w-40, no power loss, so far no failure codes, nothing at all. Zetty runs perfectly. However, i have no idea what is the reason of that sound. Some say that the valves cover should be replaced because of CСV is built in. Some say vacuum pump, but there were some examples of replacing the vac pump and still the same sound. Any ideas? Not worried, but curious.

[AlfaPlanet]

Update. Changed Mobil 0w40 with Castrol 0w40. Engine sounds a bit smoother, hydrolifter nocking, when engine is cold, on 5th cylinder gone.

[grfadi]

It must be ur CCV going bad.. causing Some Vaccum/Pressure problem in engine bay

[geoffreyolson]

That's just your bongos actuator. That's what give it its cuban beat.

[hanynowsky]

This slight vacuum pull is normal.
It should be -30mbar +-3 in N52.

[hamedh]

For me it was big end bearing. It was spun and due to friction lost thickness so there was a play. Play was about 2-3mm at TDC. I replaced the big end bearings from underneath and didn’t touch anything else, this sound was completely gone.

[Thomas-kqsd]

Why is it say like that? My car e90 say the same