[5cilinder]

Well any link of the bulletin is welcome.
But also with a rotary pump there could be pulsing airbursts with a leak, you can hear that clearly in that youtube link
And i doubt that a metal enviroment with a case on top can muffle any sound away , it acts as a channel .
The point is that there are many weak points in the vacuum track that can pull air in....the most common ones are the engine mounts....but also the brakebooster can leak or the egr bypass valve on manual cars which almost no one knows it exists and almost always go bad.
If you vacuumtest it with the engine off or with a warm engine then the solenoidvalve of the vacuum valve of the egr bypass is shut so then the leak isnt connected