Hi Folks,

First time poster here, so please bear with me. Some searching has not yielded a definitive solution, so here I am to ask the experts

91 Firebird with 305 TBI. Has a definitive whine coming from engine bay, pitch varies with engine speed (low pitch at low RPM, high at high, etc). Has a characteristic of a blower fan, but it seems to emanate from the alternator area. Brief video attached.

Anyone heard this noise before? Asking before I go deeper into problem resolution mode. I've seen how some folks replace the alternator only to yield no results. The alternator is original, though (almost all is original).

Thank you all.

 

I recommend you buy an Automotive type stethoscope and listen to each rotating accessory. That usually helps isolate any bad bearings. Harbor Freight sells stethoscopes pretty cheap. You could use a long, thin screwdriver, in place of the stethoscope, it is not quite as good, however. Be extra careful around the rotating accessories! Especially if you use the screwdriver!!

 

Late this summer I had the alternator in my 1986 Firebird stop charging, so I ordered and installed a rebuilt ACDelco alternator from RockAuto. When I installed this rebuilt alternator it sounded as though there was a toothed belt driving a blower under the hood. I wanted to keep the car as close to original as I could so i ordered a rebuild kit for the old alternator and installed the kit. Problem solved.
80-90% of the belt load on the alternator is on the pulley bearing so it is quite likely that is where your issue might be.

Notice the flanges on heads of the three machine screws for the bearing keeper are bent over after bearing replacement ,to keep the machine screws from working loose.

 

Take your og one in to a shop, prob just a bearing $20.

 

Shorted diode can make the alternator whine (and get hotter than usual) Unplug the regulator plug- and if whine stops shorted diode. If whine doesn't change,bearing is the cause.

 

Could be your wife/GF. They whine all the time.

 

Agree with the recommendation to get an automotive stethoscope and use that to pinpoint the noise. Could be a bad alternator, could be something else.

Also, take off the serpentine belt and spin each accessory by hand and see if you can hear/feel the noise/vibration.

I had a power steering pump mounting bolt back out and was rubbing against the backside of the power steering pump pulley. Sounded like a bad bearing.

 

Thank you all for the suggestions and insight. I will reply to this post with any updates and hopefully the key to success for others' benefit!