Is my alternator going out?

[df2x4]

The whining through the stereo speakers can be noise from failed diode(s) in the alternator, but can also be a poor ground in the stereo wiring - especially if it's got an aftermarket unit, depending on how it's wired in, and whether or not there's aftermarket amplifiers in the mix.

Richard

One of my dad's earlier 400s did this straight from the factory when it was new. Very slight alternator whine through the stereo when it was powered on. Seemed to be most noticeable when playing a cassette IIRC. He had it fixed under warranty but unfortunately I don't remember what the cause was... I'd bet on a ground issue though.

 

[slow_c1500]

You said “new sounds”.

Is anything else “new”, such as a recent change, ANY change, made to the vehicle… electrical OR mechanical?

Re: Alternator noise in the radio, this can be caused by a “poor or improper ground upon installation” of a new unit OR a “good ground gone bad” on an existing unit.

In the latter case, it’s possibly due to a failed or failing OE ground strap, but could be elsewhere.

It has an aftermarket radio but that has been installed for about 2 years. I’ve changed the fuel pump, and I switched the taillights, third brake light, and turn signals back to oem halogen from LED. Not sure if any of these could possibly be related.

 

[1998_K1500_Sub]

It has an aftermarket radio but that has been installed for about 2 years.

OK, so you've had no "whine" noise until recently... "new", as you said.

I could tell you how to check the alternator with an oscilloscope, but I'm guessing you don't have access to one.

Personally here's what I would try:

Disconnect the alternator plug (probably looks like this below) and see if the whine goes away. If so, it means the whine's somehow related to the alternator... at which point I would probably swap the alternator with another to see if the whine disappeared.

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Meanwhile, @jd33173 gave you some good suggestions for alternator and/or belt-related noises. The noise you're hearing MAY be something other than these, of course.

I’ve changed the fuel pump, and I switched the taillights, third brake light, and turn signals back to oem halogen from LED. Not sure if any of these could possibly be related.

I wouldn't expect these to cause a whine. However...

When you changed the fuel pump did you confirm the condition of its ground wire? I have a Suburban, and my pump grounds to the frame in the rear. On the pickups, I assume the pump grounds on the frame as well but I'm not certain of the location.

I'm not saying this is related to the whine, I'm saying it's worth checking

 

[slow_c1500]

I tried unplugging the alternator and the radio whine went away. Also when i turned the alternator by hand with belt removed, it squeaked a little bit. It’s hard to describe how easily it spun, I can do it with one finger but it didn’t spin SUPER easily.