Brand new alternator whistling at idle...

derekjl · Jan 17, 2018

At first I thought this might be normal, but now I’m not so sure. Just installed a brand new (not remanufactured) alternator, OEM AC Delco. Everything went smoothly and was very easy. However, I’ve noticed that when ANYTHING in the truck is turned on that requires electricity, a distinct whirring/whistling noise will occur. It’s definitely coming from the alternator. The previous one made a similar sound but was not only at idle, this is only if the truck is sitting. The moment you step on the gas and go above 1,000 rpm the noise stops completely. It comes back when decelerating, again only below 1,000 rpm. This gets extremely annoying, especially in stop and go traffic. Is this really considered normal? I attached a video for reference. Only my headlights and the heater are running in the video. When everything is totally off, the noise is 90% gone. This combined with the voltage fluctuation I mentioned in my other thread makes me this these 100 amp units just don’t cut it. I’m tempted to spend the $150 on an aftermarket 140 amp one, but maybe that wouldn’t solve my problem if there even is one? Any input is appreciated...

east302 · Jan 17, 2018

My father-in-law had a 94 years ago. His sounded just like that and I’ve heard other TBIs that make that noise. The vortec versions put the alternator on the passenger side. I’ve had three vortecs and they don’t make that whine. All have been the 100-amp units. I would wonder if the different placement of the alternator changes the belt geometry somehow and minimizes the whine.

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derekjl · Jan 19, 2018

east302 said:
My father-in-law had a 94 years ago. His sounded just like that and I’ve heard other TBIs that make that noise. The vortec versions put the alternator on the passenger side. I’ve had three vortecs and they don’t make that whine. All have been the 100-amp units. I would wonder if the different placement of the alternator changes the belt geometry somehow and minimizes the whine.

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I've also had three Vortecs before this TBI truck, all were '99 Tahoes with the 140 amp alternator on the passenger's side. Like you said, none of them made a whistle/whine, etc. I wonder if the noise on these trucks is "louder" because the alternator is basically "in your face" right when you open the hood, and it is on the driver's side. From what I remember, the '99s alternators were kind of "tucked away" on the passenger's side, it wasn't as high up as these are and there were components around it to maybe deaden the sound some. Like I said, the noise is only there when at least one electrical component is on, and only at idle basically. I did a google search, and it isn't all that uncommon, tons of results on BMW forums for some reason. Some people suggest checking ground connections, and possibly a draw from a low battery or battery that is on the way out.

PG01 · Jan 19, 2018

Thats too loud for normal to me. Hows the battery condition? Ive had new alternators that were bad new out of the box. That being said my plow trucks used to whine like that, only after heavy plowing, i wrote it off as alt working harder to recharge battery because it would quiet down after. How are your battery cables, grounds and belt, belt too tight? you changed the alternator because why? I would go over every ground in engine bay, check belt tension, load test the battery, check voltage at alternator and at battery with a dvm and get some crc electrical contact cleaner and shoot inside the alt, if still whining take it out and get a replacement or better yet higher output replacement. My 2 cents anyway

derekjl · Jan 25, 2018

Galante said:
Thats too loud for normal to me. Hows the battery condition? Ive had new alternators that were bad new out of the box. That being said my plow trucks used to whine like that, only after heavy plowing, i wrote it off as alt working harder to recharge battery because it would quiet down after. How are your battery cables, grounds and belt, belt too tight? you changed the alternator because why? I would go over every ground in engine bay, check belt tension, load test the battery, check voltage at alternator and at battery with a dvm and get some crc electrical contact cleaner and shoot inside the alt, if still whining take it out and get a replacement or better yet higher output replacement. My 2 cents anyway

Sorry for the late reply. The more I listen to this noise, the more I think it might be a vacuum leak. But, not sure that would explain it only happening with the electrical accessories on. Very hard to pinpoint exactly where the sound is coming from. So, I can say that I am not 100% sure it is the alternator. I do know the truck made this exact same noise when I bought it a couple months back, it was not as loud but it was definitely there. I changed the alternator because the old one crapped out, was not charging the battery, battery light was on, had barely 12 volts according to the meter. A couple things that would really help me out...1) some sort if diagram with all of the ground connections, 2) a vacuum line diagram for this particular TBI engine. I'm really at a loss with this one. Even though the whistle is at a low RPM only, it is EXTREMELY annoying especially when just sitting in park or in stop and go traffic.

JonnyTahoe · Jan 29, 2018

Take it back if your not happy and have it checked out. I got a 95 and have only ran 105 alt's. Had a New NAPA with a limited lifetime warranty start making noise after a few years. I took it back they put it on their machine and it failed some of the tests so they gave me another brand new one at no charge.

willxfs · Jan 29, 2018

I've thought about the following suggestion when trying to trouble shoot a bad engine temperature sensor or bad gauge. I never did try it...(The instrument gauge would never read above 160 or so and I was thinking of a way to momentarily and very temporarily increase engine temperature). Ok, on to the the suggestion. By removing your serpentine belt and running the engine (a very short period of time), you would eliminate all the accessories from the equation. I dont have a clue if this is somehow bad for the engine but something to think about... Maybe someone with more mechanic's experience can chime in if this is wise or not.

JonnyTahoe · Jan 29, 2018

derekjl said:
At first I thought this might be normal, but now I’m not so sure. Just installed a brand new (not remanufactured) alternator, OEM AC Delco. Everything went smoothly and was very easy. However, I’ve noticed that when ANYTHING in the truck is turned on that requires electricity, a distinct whirring/whistling noise will occur. It’s definitely coming from the alternator. The previous one made a similar sound but was not only at idle, this is only if the truck is sitting. The moment you step on the gas and go above 1,000 rpm the noise stops completely. It comes back when decelerating, again only below 1,000 rpm. This gets extremely annoying, especially in stop and go traffic. Is this really considered normal? I attached a video for reference. Only my headlights and the heater are running in the video. When everything is totally off, the noise is 90% gone. This combined with the voltage fluctuation I mentioned in my other thread makes me this these 100 amp units just don’t cut it. I’m tempted to spend the $150 on an aftermarket 140 amp one, but maybe that wouldn’t solve my problem if there even is one? Any input is appreciated...

That video you took is Great. You can definitely hear the Alternator whining.

JonnyTahoe · Jan 29, 2018

east302 said:
My father-in-law had a 94 years ago. His sounded just like that and I’ve heard other TBIs that make that noise. The vortec versions put the alternator on the passenger side. I’ve had three vortecs and they don’t make that whine. All have been the 100-amp units. I would wonder if the different placement of the alternator changes the belt geometry somehow and minimizes the whine.

Sent from my iPhone using Tapatalk

Surprised your able to hear that at a stop light. There is no doubt that its working.

JonnyTahoe · Jan 29, 2018

willxfs said:
I've thought about the following suggestion when trying to trouble shoot a bad engine temperature sensor or bad gauge. I never did try it...(The instrument gauge would never read above 160 or so and I was thinking of a way to momentarily and very temporarily increase engine temperature). Ok, on to the the suggestion. By removing your serpentine belt and running the engine (a very short period of time), you would eliminate all the accessories from the equation. I dont have a clue if this is somehow bad for the engine but something to think about... Maybe someone with more mechanic's experience can chime in if this is wise or not.

No belt and the Alt will not work either so that's not going to help any.

Brand new alternator whistling at idle...

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