It is a problem called "Perceived Noise".
The noise isn't really loud, but as has been said before, it is a DIFFERENT kind of noise.
When the garbage truck rumbles along the street at 5am and crashes the bins up and down, it wakes everybody up, but the folks know that this is an essential service, and complaining is just stupid.
When the local yobbo roars up the street with his hot exhaust, it wakes people up, but people are not game to complain as he is a member of the local yobbo gang that would set fire to your car.
But when a helicopter flies over, people perceive this as a rich boy's toy, a jetski of the sky, which must be eliminated. And because the FAA/CAA/CASA makes it so easy to complain, and even explains to people how to complain, and are obliged to respond to a complaint, these folks hop on the phone and have a moan. One person complaining 100 times (a d!ckhead making a fuss) is recorded as 100 noise complaints (ooh, lots of people are complaining - better kick these helicopters out.).
Even the sight of a helicopter is enough to make somebody think that the noise is excessive.
When we were jumping through the hoops to get our Parramatta heliport approved in the late 90s, the local Labor council thought that they would squash us by requiring noise tests with microphones at the nearest houses around the suburb which, they reckoned, would record horrible helicopter noises and stop the application.
The tests were a resounding success - for us. The sound recordings could not detect the helicopter noise from the sounds of the Western Freeway, James Ruse Drive, the gravel crusher, and the local speedway. So, the noise isn't a problem, it is just the people who don't like helicopters.