High Pitch Sound Under Hood

techjeeper said:

We are hunting a high pitch sound under the hood at idle. The sound get lower pitch and goes away as you rev the engine/push the gas pedal.

It sounds like it’s on the driver side, upper part of the engine, it isn’t there when it’s started. It starts a few minutes in after it’s either warmed up, or some system switches from start up to run. But it’s minutes not seconds every time. One time I hit a bump and it went quiet for a couple minutes then it came back. I’ll try to get a video or sound clip to post.

At idle it’s very high pitched and loud, it calms down to low whistle as it revs, then goes away over 3k rpm or so. Comes back as soon as it returns to idle.

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techjeeper said:

All factory intake system.

It can try the belt but it’s not a squeal like belt. It’s way higher pitched and also sounds like air or vacuum but it it gets lower when vacuum increases as you rev. I’d think it would get higher when you add RPM or throttle. It’s really got stumped right now. I unplugged each vac port I could get my hands on and no real change other than it follows the Rpm when you unplug a vacuum port.

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