D.W.
My almost-5-year-old did the same thing and also had big problems with my hair dryer and with those electric hand dryers in public restrooms (which made for lots of issues with wet hands once she was potty-trained). For her it's definitely a noise thing. She still needs to be in her room with the door closed if I'm vacuuming or blowdrying my hair, although she's starting to be willing to use the hand dryers now. Truth be told, part of why I hate vacuuming myself is because it's so noisy and I can't hear anything else while I'm doing it.
22 months is also prime time for separation issues and concrete thinking development. He might have noticed that things get sucked up into the vacuum and don't come out, and is worried that that will happen to him, too. I know this happens for lots of kids about the toilet also. Maybe you could try having him watch you empty the vacuum canister or change the bag or whatever?