Sounds like it's the PCV diaphragm making that noise, although I wonder if the oil trap was bolted down correctly and has a good seal. You might have a small vacuum leak somewhere.
Noise from PCV diaphragm when dipstick pulled
https://www.matthewsvolvosite.com/forums/viewtopic.php?t=93071
Goose Honking Sound-PCV Disc...UGH (2004)
https://www.clubtouareg.com/threads/goose-honking-sound-pcv-disc-ugh-2004.222674/
I take it when the engine's running and you pull out the oil dipstick or loosen the filler cap, there isn't an overly strong vacuum? (This might trigger a check engine light, but it should go out again.)
