My 2006 2.0 litre turbo volkswagon passat started making this very loud whistling noise yesterday evening when i left owrk. The car had warmed up and I start hearing this noise. What could this be? No check engine light has been displayed either.

inside gas tank

indicates faulty injectors
have they reconditioned and calibrated by an accredited diesel specialist shop

if you have shop air pressurize after the turbo ,make soapy water . find leak visually, whistling noises often mean leaksso then turbo pressure dissapears//gentle please turbo does not break 50 pounds of pressure whith

A bearing going bad. Do you follow turbo shut down procedures? If you don't have time to do this then my suggestion is installing a turbo timer to do this automatically. When you drive the car specially a high speed and need to shut down the engine is the worse thing you can do to your turbo. The impeller spins double the speed of sound and takes quite a while to slow down specially when you shut down the engine. At the same time it is shut down, oil pressure is no longer provided by the oil pump and cooking from extremely hot turbo assembly. The end product is oil carbonizing and clogging moving parts. The term is called coking. A turbo timer will keep your engine running when you remove the key from ignition and lock the vehicle for a programmable amount of time. This will help the turbo to spin dow while lowering the temperature critical for a longer servie life of your turbo charger.

Remember, what is heard as turbocharger noise may not be caused by a noisy turbocharger. Before replacing a turbocharger perform the following diagnosis.
A. If a loud whine or whistle is heard during acceleration and increases or decreases with rpm and load. This condition is most often the result of a loose clamp/hose at the turbocharger compressor outlet, charge air cooler inlet, outlet or at the intake manifold.

1. With the engine running at idle and the transmission in Park or Neutral with the parking brake set, feel for boost air escaping at each connection between the turbocharger compressor outlet and intake manifold. For limited access areas, spray soapy water on those connectors and look for bubbles.

2. Check the exhaust manifold and exhaust system for leaks.

I hope this helped.

Thank you,
Norse

hallo
if power steering fluid is bubbly, means that its sucking air somewhere before(sucking side) (or on) power steering pump. that would explain the noise. Check (when cold) fluid level. if level is low, top up before starting the car. had a lot of cars that high preasure hose was leacking fluid on restricting valve. if so, fluid comes out on the end of protecting cover of the hose. (driver side on spark plugs and down the engine). replace hose with original. do not try to make it your self, becouse steering wheel will shake, sinse restracting valve is missing.
But if you press brake pedal, that has nothing to do with it.
Marko

check pipe connected to turbo it maybe split/also turbo unit itself may need replaycing/fan inside turbo maybe worn

Spark plug blow out?

Check your power steering fluid reservoir.

Ignition coil or wire set?