My cowherd has always been fairly calm, we live in a heavily traveled state road, with around a mile road frontage. They are used to a lot of different sights and sounds. We 2 different neighbors across the road that evidently do quite a bit of shooting particularly around hunting seasons, and another situation towards the back of the property on another road that sporadically will shoot like they are target practicing too.
There are often helicopters be it medical transport, utility companies checking power lines, or military helicopters flying over. Generally speaking they don't bother the cattle. At times there may be some unease like if the utility ones are coming in low to the ground and kind of hovering around low and making odd movements instead of just going straight over like a normal flight path and height.
We have a lot of folks living around us so around 4th of July it sounds like a war zone around. That can cause the cattle sone unease at times too. Once I noticed it really scaring the neighbor's horses they were running frantically from one side of that property to the other.
I've found that my cattle don't take to strangers around. I can walk through them and have anywhere from 10 foot to arms length flight zone, and at that they slowly walk away keeping a feet between, but if somebody else other than my wife is around that flight zone might be 50 feet and they move pretty fast.
Younger cattle in my experience seem to be more easily spooked than cows.
Ive had a group of probably 4-6 month old Holstein calves spook and about run over me because a couple coyotes were trailing them.
Sometimes something as simple as a barn door having ice on it and making a cracking sound when the ice breaks when trying to get the door to open, that has spooked a many a bunch of feeder calves (stocker calves, for folks outside of KY), both Holstein and beef calves.
I think a lot of different sights and sounds bother them at first, but they get used to most things except the weather/ice related, or something that happens infrequently and catches them off guard.
Over the years I've noticed one thing that startles any cattle of any age that I've had, and that is if a truck or trailer has a loose tarpaulin that is flapping around, that noise will at them off and cause them to run over the hill ever time.