high pitched sound

[9901gp]

I just got a 99 GTP and I hear a really high pitched sound coming from under the hood, like a whistle. Sometimes I dont hear it and its louder at idle. Could this be a vac leak? Has anyone heard of this happening. Any opinions would be appreciated.

[BNaylor]

Welcome to AF.

It would help to post your mileage.

It could be a vacuum leak so check all the vacuum lines at the throttle body, supercharger, fuel pressure regulator and the evaporative emissions system. Also, you can run an engine vacuum test to see if vacuum is in specs or determine if it is really a vacuum leak. 15-22 in-hg.

[9901gp]

Thanks for the advice, and it has 26000 miles on it but its been sitting for a while

[tblake]

wow, 99 GTP with 26,000? Did I read that right?

Is the whistle only while your motor boost? It could be normal.

Could we get a video or sound clip?

[9901gp]

yea only 26000 it sat for a while, i hear the noise during idle and when i give it some gas, its louder during idle. Its weird because sometimes there is no noise at all. I will post a video once i get a chance.

[BNaylor]

The mileage is one thing but age is another factor. This is a 10 year old vehicle. Rubber components like vacuum lines and gaskets go with age not just mileage.

How would you better describe the sound? Is it more of a whistling sound or whine. Other common sources of noise could be any component in the serpentine drive belt system like an alternator or tensioner/idler pulley. And of course the supercharger will give off a whine depending on boost conditions.

[9901gp]

It's definately a whistle sound not the basic supercharger whine sound. It sounds like air leaking out of a tight area its a very high pitched tone. Sometimes it's louder and i can hear it inside the car. Sometimes I don't hear it at all.

[BNaylor]

Maybe you can further isolate the source of the noise. It would not hurt to check all vacuum line connections if you already have not done that. Also, check the throttle body mounting bolts or any component in the air intake system. For alternator you can remove the serpentine drive belt and run the car for a short period of time, preferably at idle only. Just make sure your battery is fulled charged up before doing this type test. Plus you can safely run without the supercharger drive belt hooked up.

[richtazz]

Under the cover marked PCV valve, there should be a spring, the PCV valve and an o-ring seal. Many people forget to replace, reinstall the o-ring and the resultant vacuum leak will cause a whistle. If the seal is missing, it's GM #25534756, or you might be able to match something up from an o-ring assortment at an auto parts store.

[shanger78]

i believe i have the same sound. it is under boost and changes pitches the more boost there is. it sounds like the straws you had as a kid that oyu could blow in and drive your parents crazy. the harder you blow the higher the pitch. my car has 170k miles on it.