1999 k1500 Chevy Suburban LS 350 V8 4wd. Bought from a neighbor who has since moved. Started making a strange sound....thought it was belt or pulley related. Changed the belt, Alternator, idler pulley and tension pulley.....no change. Removed belt, sound still there....so it's not belt or pulley related.....strangest sound I ever heard.

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Any idea on what it could be?

Thanks.

 

A one minute video and you couldn't even blip the throttle to see how the sound changes with engine speed?

 

Good point....the sound seems to go away when I give it some throttle, but this is when the belt is on and with the fan running so it's a bit hard to tell.
I'll have to go through the warmup process to where it makes the sound, then remove the belt and see if it changes when I hit the throttle.

 

This video is of the sound, with no serpentine belt and some throttle. Thanks.

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Ok, so it's probably not a mechanical noise in the engine, since it doesn't change pitch with engine speed.

Are you sure it's coming from the engine bay? I'm almost inclined to guess fuel pump, since it goes away with some throttle.

Try turning on the ignition (turn it to "run"), but not starting the engine. See if you still hear the noise.

 

It only makes the sound when the engine is running......no sound when engine is not running and key is in the on/run position. Sound does appear to be much louder under the vehicle.....Thanks.

 

When you figure this out be sure to update. Did you check to see if the crank pulley is rubbing on something? Does it have a mechanical fuel pump? An exhaust leak? Intake leak at the air cleaner etc..?

 

Noise changes/disappears when I open the oil cap or remove PCV .... replaced PCV about 6 months ago. Seems like there is too much pressure in the engine.....any ideas? Thanks.

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1999 k1500 Suburban 5.7 4x4......replaced the PCV VALVE, no change......strange noise seems to be related to the "gizmo" that the PCV Line connects to......Haynes manual no help.....any ideas? Thanks.

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Maybe that line is clogged downstream. Inability to relieve pressure in the crankcase will cause a blown main seal. Don't fool with that.