At our gliding club we are very aware of the noise of our tug aircraft. We use robin DR400s in the main fitted with 4 blade props and hush kits. They are very noticably quieter than the standard aircraft with a 2 blade prop we occasionaly use in competitions.
Why the average spam can is quite so noisy I cannot understand. Modern road vehicles are fitted with effective silencers so why cannot aircraft?
The pitch of the noise is also a factor. 2 stoke engines ith a 2 blade prop are particularly anoying.
Having said all this the modern 'sperm' shaped light aircraft with water cooled engines are remarkably quiet
As a biker also i feel qualified to coment on their noise levels. Standard exhausts tend to be acceptable but far too many fit 'performance' or 'straight through' exhausts. The Harley Davidson poser crowd seam to be particular offenders.
Sit in your garden on a summers day and what do you hear? In my case the distant roar of trafic, kids playing, birds singing. All of which are constant and the brain filters them out. The intermitant noises stand out. A helicopter flying by, emergency service sirens, dogs barking.
A classic example of this is when a woman has a baby she seams to rapidly become deaf to the noises. A visitor is soom wincing.