Whistling from engine bay?

[derekjl]

This sound has me puzzled. It reminds me of the sound your speakers will make when you have an electrical/stereo issue. It is definitely some kind of whistle. The pitch changes with the engine RPM. It's mostly noticeable only at idle or slightly below 1,000rpm. Could the radiator fan cause some kind of whistle with the air it moves? I also have the original alternator with what looks like metal fan blades, not sure if those "blades" can also cause this sound. Any input is appreciated. Picture of alternator attached for reference...

 

[Todd R]

Altenator or vaccum leak. Spray ether around the intake and vaccum lines and listen for RPM change. You should be able to narrow it down.

 

[derekjl]

Altenator or vaccum leak. Spray ether around the intake and vaccum lines and listen for RPM change. You should be able to narrow it down.

I’m fairly certain it is the alternator, it whines like a supercharger lol. My resting voltage is barely 12 volts, lights dim, flicker sometimes, etc especially in cold weather. I have a brand new alternator on my work bench, just haven’t gotten around to installing it. I probably should have gotten a Power Master 140 amp, buy went OEM with an AC Delco, was only $85 on Amazon.


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[east302]

Every now and again, someone posts about this and it's usually someone with the TBI (88-94) 350 it seems.

My father-in-law had a 94 years ago and it would have a definite whine or whistle to it, especially at idle with a higher electrical load--lights on, etc. I assumed that it was just something with the alternator. I've never noticed that sound on the three 350 vortecs I've had but have heard it one more than one TBI.

I think the alternator location is different on the TBI (driver versus passenger side on the vortec), so maybe the belt geometry has something to do with it. Who knows.

Check the alternator output with all accessories on and no accessories on. See if output changes, just to make sure that it isn't some accessory (blower, etc.) drawing too much.