When Beau was a pup I started acclimating him to the noise by just leaving the vacuum running in another room, and carrying on as usual in the one we were in. Once he was relaxed with that, I would turn it on in one room and bring him into the room with me, again ignoring it and going on about other tasks. Eventually we got to the point where he could care less if it’s running anywhere, even right next to him.
I turn it on when I’m brushing him, to collect the hair from the brush, and he actually enjoys that. He gets all happy when I vacuum now, hoping some brushing is coming up. He doesn’t investigate the machine, though, he seems to see it as my thing, so no need to mess with it.