For 1990-2009 cars

Cause | Correction
--- | ---
Some whine noise is normal. Compare to a known good vehicle.
Leaking charge air cooler/pipes/hoses | Inspect for leaks in charge air cooler/pipes/hoses
Worn turbocharger bearings | Visually inspect for evidence of compressor wheel to housing contact. If the turbocharger bearings are worn or damaged, inspect for a Turbocharger Lack of Oil Supply.
Intake system leaks or obstructions |

1. With the engine off, pressurize the intake system and inspect for intake manifold leaks.
2. Inspect for obstructions in the intake manifolds.