What is a "flapping sound"
Birds?
that would be the wings, like all flying insects that make a buzzing sound.
When an insect flies, the size of its wings and the speed of their flapping affect the sound they make.
There are a number of reasons why your car may be making a whirring sound when accelerating. You may have a lose part for example.
From the sound its wings make from flapping so fast. It sounds like they are humming.
Check the coolant system to make sure you are not low. An air bubble going through the heater core can make an odd sound.
Bees do not scream but they do buzz and make a vibrating sound. This buzzing or vibration comes from their wings flapping so fast when they are flying.
Transfer case is shot.
If you get enough butterflies flapping their wings in the same area it creates enough sound to be detectable. It sounds a bit like falling rain or birds flapping their wings. Otherwise butterflies are essentially mute and don't make any sounds by vocalizing.
Sometimes you can hear flapping, but mostly they are just too far away to hear it. Birds of prey tend to glide in when they attack so that their prey cannot hear them flapping and escape.Examples: owls make a soft shushing sound when they fly and mourning doves make a chirping sound that is actually their wings touching together on the down-stroke.
Well, I'm not sure what you mean by a brushing/flapping sound but if you mean it kind of sounds like the whirring of a washing machine, check your lug nuts! it was happening to me for a while and 3/5 of my lug nuts cracked off in my hand!
got youtube.com and type in "Orgami flapping bird" and the select the first video you see
your wife