high pitch whistle noise when let off gas coasting when car is warmed up

[stephenxchen]

hi guys,

I have a 2007 A6 C6 4F engine, automatic, base model.

symptom: when car is warmed up, and when coasting (RPM between 1000 - 2000), a sharp high pitch whistle noise comes from front of engine. noise disappears when accelerating, it also disappears after about 3-5 miles driving. It doesn't matter if it is in Neutral or in Drive. Sometimes can hear the noise even when car is in full stop. Yesterday, I shut the engine off when coasting, still could hear the noise.

it is a metal grinding whistle/chirping noise,definitely from the front of the engine, sounds like a bearing.


I have already replaced the following:

Water pump
Idler Pulley
Belt Tensioner

Upon inspection, steering pump seems working perfectly fine, no leaks. alternator is charging fine. no codes, no vacuum leaks,

I am at wits end. any ideas? please help.

oh, by the way, it would be very helpful if you can tell me WHY you think a particular part is causing the problem.

thanks in advance

[SinCityA6]

If you can hear the noise when the engine is off but coasting, then it is not coming from the engine. I could be many possible things; wheel bearings, brakes dragging on the discs, etc. best suggestion would be to get the car off the ground (on a lift) and try and duplicate it while someone is outside/under the car.


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[stephenxchen]

If you can hear the noise when the engine is off but coasting, then it is not coming from the engine. I could be many possible things; wheel bearings, brakes dragging on the discs, etc. best suggestion would be to get the car off the ground (on a lift) and try and duplicate it while someone is outside/under the car.


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thanks for the response.

I don't think it is wheel bearing or brake related, because when the car is fully stopped, sometimes when I rev up the engine, then release the gas paddle, I still can hear the noise.

[SinCityA6]

As you stated in the original post, you turned the the engine OFF while coasting and still heard the noise. This doesn’t make any sense.
If it is happening when standing still as well as coasting with the motor, etc. I am starting to think transmission related specifically torque converter. It is the only thing spinning in all of the scenarios you have described. But it would be coming from the back of the motor and not the front.


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[stephenxchen]

As you stated in the original post, you turned the the engine OFF while coasting and still heard the noise. This doesn’t make any sense.
If it is happening when standing still as well as coasting with the motor, etc. I am starting to think transmission related specifically torque converter. It is the only thing spinning in all of the scenarios you have described. But it would be coming from the back of the motor and not the front.


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thanks for the reply.

I, too, thought about transmission, but..... it still makes noise when the car is fully stopped. so .....


any other ideas?

[SinCityA6]

thanks for the reply.

I, too, thought about transmission, but..... it still makes noise when the car is fully stopped. so .....


any other ideas?

Torque converter is still spinning while the car is stopped and idling....


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[stephenxchen]

Torque converter is still spinning while the car is stopped and idling....


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thanks again.

question, if it is torque converter:

1. why is it temperature sensitive? it doesn't make noise when cold, only when warmed up. BUT, after a few miles, it goes away, too.
2. why does it still make noise when in neutral gear?
3. why does the whistle "usually" stops when the car is stopped? (again, sometimes it still makes a few seconds noise when just stopped, then it goes away)

thanks.

[stephenxchen]

the high pitch whistle sound is similar to this:

https://www.youtube.com/watch?v=OFb1Mt_8H08

[SinCityA6]

So that video sounds like a bearing on an accessory pulley or shaft going out. But you said you hear it when coasting with the engine off. If nothing is spinning with the motor off, a pulley or shaft bearing is not your issue.


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[SinCityA6]

thanks again.

question, if it is torque converter:

1. why is it temperature sensitive? it doesn't make noise when cold, only when warmed up. BUT, after a few miles, it goes away, too.
2. why does it still make noise when in neutral gear?
3. why does the whistle "usually" stops when the car is stopped? (again, sometimes it still makes a few seconds noise when just stopped, then it goes away)

thanks.

The torque converter is filled with fluid. Cold fluid is thicker than warmed up fluid so that may explain why the sound appears as the fluid is warming up and then disappears once it reaches full operating temp.

I am in no way an expert, but just trying to reason through the possible causes.
Here is a decent video that describes the parts and function of a torque converter.
https://youtu.be/WUFNySTjUmQ


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[stephenxchen]

I tried to reproduce the while while coasting with engine shut off, but was not able to duplicate the issue. May I was wrong about that, it's been a while.

[jdaudi]

Check piping from airbox to intake