My 8 cats have varying opinions on the vacuum. Jack will hiss at it if he even sees me wheel it out, even before it's plugged in. Dusty will sit while I vacuum as long as I don't bump whatever she's sitting on. Bear will let me vacuum him with the hose, does a great job getting up loose hair off him.

For those that really are afraid of the vacuum, just shut them in a room BEFORE you even get out the vacuum. And if you need to vacuum that room, then just move them to another room before you vacuum that one. The door being shut should be enough to muffle the nosie, also playing a radio or tv kinda loud in that room should help some.

Good luck.