Whining alternator on my ‘94

[TruckerDad23]

I’ve read through the threads about whining alternators here and had no luck so I figured I would post my own. When I got my 94 the alternator was whining(it stops when you unplug the connector with the brown wire).
Instead of replacing it right away, I bought a new set of diodes and replaced those but nothing changed so I bought a brand new AC Delco 105 amp unit.
It still whines. Up and down with the RPM. I even checked all the grounds and cleaned them up. I’ve seen some people on here say that they’re alternator whine went away after 1000 miles or so but mine’s still going at around 4000+.
Has anyone been able to find a solution to this other than buying another alternator and hoping it doesn’t do the same thing? I feel like there could be a solution having to do with the brown-wired connector or maybe a heavy duty ground directly to the alternator case but I’m not sure.
Any help would be appreciated.

 

[GoToGuy]

Your sure it's the alternator, not a worn belt, slight pulley misalignment, idler pulley, tensioner vibration. Have used a stethoscope to really narrow it down.
I know mine makes a little more noise when at night with headlights on, nobody else hears it, but after so many years you what's normal and what's .... different?
Not that your mistaken , but installing a new component and the same sound continues, broaden your search area maybe. Harmonics vibrations can be tricky to pin down. Good luck.

 

[Schurkey]

Have you put a multimeter and amp-clamp on the alternator to verify output voltage, output amperage, AC "Ripple", etc?

Are you hearing this whine from the alternator directly, or via the radio/stereo in the truck?

Have you removed the belt, and spun the rotor to see if the bearings are rough? CS130s used to be infamous for cooking the rear bearing.

 

[TruckerDad23]

It’s definitely the alternator itself. I can remove the single-wire plug and the noise stops.

 

[Alteca]

Have you had battery issues? Old battery? Sounds like it’s under heavy load. Maybe it’s a long shot but it could be another bearing whining(AC clutch bearing, power steering,etc) and when you pulled the plug on the alternator, the reduced load caused the whining to go away. I know you said it’s for sure the alternator but I’m just throwing potentials out there

 

[sntrym]

CS130s used to be infamous for cooking the rear bearing.

They still are. Ask me how i know and why I keep a spare alternator handy

 

[TruckerDad23]

Have you had battery issues? Old battery? Sounds like it’s under heavy load. Maybe it’s a long shot but it could be another bearing whining(AC clutch bearing, power steering,etc) and when you pulled the plug on the alternator, the reduced load caused the whining to go away. I know you said it’s for sure the alternator but I’m just throwing potentials out there

Thank you for the suggestions. This is the first thing in a while that’s given me a new road to go down.
I’ll update if I find anything.

 

[tinfoil_hat]

Half these answers assume you are describing a mechanical noise, the other half assume you are talking about radio interference. Which is it?

 

[TruckerDad23]

Half these answers assume you are describing a mechanical noise, the other half assume you are talking about radio interference. Which is it?

It’s mechanical from under the hood.

 

[TruckerDad23]

It’s mechanical from under the hood.

Also, sometimes the volt meter wavers up and down a volt or two.