my cat is absolutely terrified by the street cleaner that goes down our block a few times a week. the vehicle makes this kind of low vibrating noise as it eases down the road at like, 5 mph, so there is a bit of a rumbling in the bedroom when it's outside. but dude, if you were a cat, and you spent 24 hours a day in the same relatively small area, i would think certain things wouldn't surprise you after a while. perhaps you'd come to certain conclusions, things like "the street cleaner is not going to eat me" and "the vacuum cleaner is not going to eat me" and "i am never in any sort of danger at all, i always have food, water, and comfortable furniture to sleep on, so i should stop being such a fraidy cat". this just will not do for no-alarms-and-no-surprises larry, good thing she's the cutest cat in the world. :)