Faint whistle noise when accelerating
 

Hey guys,
Anyone else experiencing this when accelerating? It is a faint whistling noise and it sounds louder when it is colder. Ive gotten use to the noise now but it is still existent. Could it be the turbo?

It's not effecting performance so I am not too worried that its a vacumm leak.

A4 1.8t Quat 2004

Is either your turbo spooling or your SAI, the Secondary air pump comes on when you first start the car to stabilize the air/fuel mixture.

Car you hear the noise when reving the engine? I mean, is it RPM related or speed related?

I know this thread is over a year old but did you ever figure out what it was? My car has no turbo and it makes a whistling noise upon acceleration. It does not make the noise if just rev it up, only when im in gear accelerating.

Update:
The whistle noise has continued upon acceleration and my turbo was lagging slightly. Wasn't bothering me too much and thought it was normal. Until my CEL just came on last week, open the hood and the whistling noise is louder even in idle. Assumed vacuum leak somewhere. My RPMs were jumping and in park, sits at 1200 RPMs.

Noticed the high pitch whistle noise from a black hockey puck looking thing. Started moving hand over area and noticed a hole in which air was escaping/being sucked in causing the noise. It is the Pressure Regulator Valve-
Valve that sits in the intake hose that goes down to the turbo inlet
06A129101F - Part Number - Ordering it from ECS and is in transit. Will update once I install the new one. Hopefully that is the problem.

FYI - Oh yeah the codes from the CEL was ...

P0507

Idle Control System Higher than Expected

P0171

Fuel Trim,Bank1 System too Lean

You my friend have a big Vaccuum leak. Search on the interet for a Audi A4 leak detection and you will find some DIY how to find the leak.

Update #2: Replaced the PRV since it was sucking in massive air and car runs much better! The old PRV had slight oil inside which was strange?! Idles great now as well. Cleared CEL drove about 5 miles. CEL comes back on with same 2 codes PO507 P0171, but the car is running much better than before. Another leak somewhere? or does the car take awhile to adjust to new PRV i just put on. I will clear it again and drive throughout day.