Why do most A320s make that distinct scream on takeoff?
The whining noise is generated by the rotating components in the engine. At takeoff power for an engine of that size, the fan is rotating at about 5200 rpm. This is about 86 times per second. There are also 22 blades on the fan at the front of the engine. This means a given point sees a fan blade pass about 1900 times per second. Each fan blade changes the pressure as it passes, resulting in a tone of about 2kHz. This is the whine that you hear. At takeoff the tips of the fan blades are going supersonic, each one creating a shockwave.