When I vacuum, my kitties get upset.

The little one simply runs away as soon as we open the closet where the Loud Monster lives. She hides under the covers and doesn't come out for hours. She assumes that we, the humans who provide for her every need, will keep the Loud Monster from finding her as she curls up with her paws in her ears, purring the kitty version of "I can't hear you!"

The big boy, on the other hand, chooses to keep the Loud Monster in sight for the entire time that it is out. He follows it around, staying just out of reach. He looks brave, but he is really terrified. This is obvious by the way that he occasionally swats anything that happens to be near him. He seems to be saying "That loud noise is really scary. I know that big machine is responsible, but I am unable to defeat, or even approach, the Loud Monster. In the meantime, this empty shoe is just asking for a beating." His feelings of fear and impotency are so overwhelming that he has to lash out at the nearest object, even though he knows that the shoe really isn't connected to the Loud Monster that is causing the feelings.

Neither of my kitties has a very effective or healthy way of dealing with the Loud Monster. But THEY are cats.