I can't even tell you how many times in the military, firing had to be stopped at the range while someone in a hummer had to drive the deer and turkeys away. My hunting grounds are one ridge away from a range and out of state bowhunters often express concern about all the shooting going on spooking deer. Of coarse it's everyone in the county sighting in before rifle season and competion shooting going on in the next valley. I assure them that the deer are used to it and after they see the deer ignoring it completely they settle down and hunt. I have also witnessed deer standing and watching me as I sight in or use a chainsaw. These noises are so common that they are ignored as long as you don't look at the deer. Once you stop your normal activities and stare at them then they will spook. It has little to do with sound and everything to do with a predators attention being rivitted upon them. I was watching bulldozers work the other day pushing brush and so were the deer, until I noticed the deer and looked directly at them, then they left. They are very curious and until they are scared away by a predator watching them they will investigate strange sounds. They can even get used to that in a park setting where people watch them all the time and leave food for them which is why baiting is not allowed in some places.