How do I Identify Turbo Noise from the Audi A4?

1. Start your A4's engine, take it for a drive and locate a straight and empty area of road where you can accelerate safely, such as a country road or highway on-ramp.
2. Depress the gas pedal to the floor to rev the engine, which will apply air pressure to the turbocharger and cause it to spool and produce its distinctive sound.
3. Listen for a high-pitched sound, similar to that of a vacuum cleaner, coming from the engine bay as your engine's rev level travels from approximately 3,500 rpm to its maximum rev level.