When I had my 14 year old Beagle/Bulldog mix, she would always run away and hide in my room whenever my mom would vaccum. Now I have two cats that aren't so much as fazed by it. Hell I had one time when my older fatter cat was sleeping on the vacuum WHILE I was using it. didn't even wake up until I finished and he sluggishly walked off only to lay back down in the hall I need to go :/
my grandma has a HELLA old vacuum that basically sounds like it's yelling, but, we've taken carpet out of the living room and hallway, and our rooms are so packed we can barely see the carpet left in there.
Oh my gosh, my dad used to do that at night ALL THE TIME. We got him one of those little hand-held vacuums for his birthday....big mistake. He stays up late sometimes and if he sees dust or something, he'll just get this weird urge to start vacuuming. That noise is just so awful.