Whistling/humming Noise

[canuckz71]

Not sure if this is the right section so someone can move it if not.

Anyways, about 2 weeks ago i started hearing a whistling/humming noise from the truck that sounds like its coming from near the heater core but i dont think that's the problem. The whistling is fairly loud and gets louder/higher pitched when the rpms increase. Also it doesnt matter whether the fan is on or off it still makes the noise.

Its getting warmer this weekend so ill have a chance to take a look at a few things before its goes back to freezing cold but I'm not sure where to even start. Any suggestions or other experience would be awesome!!

 

[Mean Green]

A possible exhaust manifold flange gasket "Donut" could be the problem depending on what the noise sounds like. It's fairly common for the donut to go bad, although in general when they are first starting to fail they will make an almost tick sound. You may want to take a look at that!

 

[canuckz71]

Heres a real bad video i took on the way home from school on my phone, its pretty quiet so you might need to turn your speakers up a lot. But you can hear the high pitched sound.

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[Tempted]

Probably your alternator.

 

[canuckz71]

I dont think that's it the noise isnt coming from the alternator. Could be a vaccum leak somewhere? Although wouldnt that effect how it runs? It runs just as well as before this started

 

[Tempted]

Sounds like the alternator to me One of the well educated techs will explain it to you I'm sure. I don't have enough credibility on these forums yet to go into a detailed diagnosis. Pop the serpentine off, crank the truck, see if the noise goes away. Obviously don't run the motor more than a minute. If the noise goes away, replace your alternator.

 

[canuckz71]

Alright I will give that a shot thanks

 

[canuckz71]

bump!

looked at the alternator and that doesnt appear to be it...any other suggestions?

 

[Tempted]

Well the reason I am betting on it isn't because of anything you would see or hear at the alternator itself. It is called RFI, radio frequency interference. An alternator has diodes to counter RFI and when they go bad they cause a hum, or whistle, which sounds like it is coming from the speakers(under the dash). This is one of the very few things that will raise and lower in volume/frequency with the change of engine RPM. That is why I suggested popping the belt off and running the truck. Take the alt out of the picture. If that isn't it, you should hook up a vacuum gauge and make sure you are pulling 16+ at idle. If not, you may have a vacuum leak and it, while it would be extremely uncommon, might cause the hum you are hearing. When you give an engine throttle the vacuum decreases to nearly zero, not increases. This is why vacuum leaks are most heard at idle and not when you raise the RPMs. Hope that helps some. Lots of smart guys on here, I'm sure someone will figure it out for you. Just keep us updated on what you have tried.

 

[canuckz71]

Well, you were right temped I took the belt off yesterday and the noise went away so I'll need a trip to NAPA. Thanks for the help!