When starting my vehicle and beginning to drive, I get an odd sound from the engine or transmission during shifts. Its on top of the normal revving sound from the engine. It sounds like a high pitched rev. It only makes the noise if I'm pushing over 1500 rpm's. Whats even more odd is that the sound goes away after a couple of minutes of driving. It shifts through all the gears without any unusual noise. It's only around for a cold start. Any input would be appreciated as to what might be the source of that sound.


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1999 Chevy Blazer LT 4.3L Automatic 2WD

 

Two things come to mind. Either the power stearing pump or the transmission pump. You can try opening the hood starting the engine when cold and moving the throttle by hand so you can listen to the power stearing pump. I suppose if you want to try crawling under the started vehicle you could listen to the transmission pump as well. You would need a trusted assistant for that. If it does not do it unless moving I would shift the odds towards the transmission.

 

Does it sound like a tinny vibration, like a heat shield that is loose?

 

The transmission pump sounds like a good place to start since the sound seems to follow along with shift points. The noise starts about seven seconds from the beginning(the engine is just a picture, not a video of engine running) of the audio file. I recorded the sound if anyone has heard it before. Might have to turn up the volume on your speakers to catch it, but the sound is there. Maybe it will help.

Engine Noise - YouTube

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1999 Chevy Blazer 4.3L Automatic 2WD