It is completly normal. Rabbits know pretty well what noise is a hint for danger - and no predator is loud. I have to take care to keep the rabbits away when working with the chain saw or chopping wood, and on New Years Eve they are just happy that someone is up at midnight to give them a snack.
A twig breaking, leafs rustling, a bird sounding an alarm - this can set them on high alert, what sends them running though are fast, unexpected movements.
Anyway, as been said, their hearing is pretty good, and I would avoid really load noises around them even if they don't bother them. At work I'm used to wearing ear protecion, and for me many household machines are well above the level when I put muffs on. And that would be a good idea for everyway, the small damage accumulates and will show with age.