tires
The pitch of the propeller causes this noise.
are you sure is a valve noise?? or is a piston slap?
will tires make noise if there choppy on inside
What causes the a squeak in my showtime rotisserie
what kind of noise?
if there is a creaking noise in your car, i think that's bad...
Brakes
Something that is lethal that causes no noise.
The fuel in the cylinders exploding
It is the alternator....
in most schools it has to do with the horns of the bus rarely the students own noise of playing