Why do some airplanes make noises that sound different or are louder than other airplanes?
There are many different types of aircraft that fly today. Each type has different features and capabilities. Some aircraft make more noise than others because of the type of engines they have. Also, larger aircraft tend to make more noise than smaller aircraft, though this is not always the case. Your proximity to the aircraft affects the volume of sound you hear. The volume of noise also depends on the age of the aircraft creating the noise. Newer aircraft have newer engines and designs which are quieter due to evolved technology. Different engines and airframes have entirely different noises associated with flight. Please refer to Sources of Aviation Noise and Noise 101 for more information.
