2001 Jimmy - Vacuum Noise under hood?
 

Hi folks,
I have a 2001 Jimmy, 150K fully stock 4.3 vortec. Occasionally I hear a humming vacuum like noise coming from under the hood. The only way to get rid of it is to turn off and restart the truck. This usually works 95% of the time. The noise may not come back for days or until the next stop, and start of the engine..

It does not sound like a belt whine or anything like that. More like a kettle whistling (but not as high pitch). All vacuum lines look good, but why would it stop and start if I shut down and restart the engine, say at a red light?

Any help would be greatly appreciated.....

Thanks in advance :-)

I can't give a definite answer but my 96 Jimmy does the same thing on occasion. I describe my noise as a rushing wind sound which happens on start up on a cold engine and goes away when it is warmed up. I have always assumed it was the fan clutch engaging when is probably shouldn't. Just a guess.

Not sure, you may have to see what part of the engine bay it's coming from. Possibly EGR or Charcoal canister venting?

Fuel lines??? I had my supply line replaced and ever since it makes a vacuum noise... When it warms up or the lights are on the noise quiets down for some reason.