Alternator whine - but its not the usual suspects....

[Jimxms]

Ok guys I did some more testing today, and I'm still stumped.

* I sprayed water on the alternator pulley and belt. It didnt make any difference to the noise, making me less suspicious of the belt.

* Then I connected jumper leads (both + and -) direct from the alternator to the battery. No difference. Note: I forgot to disconnect the alternator wire though...so this may be a false test.



* Then i plugged in my OBD2 scanner, and checked the BCM for charging data. It appears to be pulling about 60A:



I wanted to double check this with an amp clamp, but unfortunately I only have an AC one, so it didnt work.

* Then I checked for tensioner markings. I couldn't find anything definitive, so here are some pictures:



* Finally I Ohmed all of the cables and routes that power would take:

Positive Wires
+ Wire that goes from alternator to fusible link = 1.8ohm
+ One side of fusible link fuse to other side of fuse = 3.1ohm
+ Positive battery post to battery side of fusible link = 3.4ohm
+ Alternator post to positive battery post = 10.2ohm

Negative Wires
- Alternator body to chassis post on firewall = 7ohm
- Engine block to random bolt on body = 5ohm
- Battery terminal to engine block = 4ohm

 

[j91z28d1]

sadly the ohm reading doesn't tell you much, even thou some of those do seem a bit high, but could just be the bolt heads and probe not making perfect contact. the meter just runs a small amount of voltage thru the wire, it doesn't give you much idea of what's happening with 60amp running thru it.

this is a simple way to give you good info with just a standard volt meter.

shame about the meter but if the obd reading is correct, 60amps shouldn't really made it whine.

I'm kinda out of ideas. maybe some others can help.

 

[Jimxms]

Bit of an update....I did the "big 3" upgrade using 0/1AWG wire and i think the noise has decreased. It seems to only whine (but at a lower level) for a few minutes at startup and then by the time I'm on the freeway its no longer noticeable.

I guess my question now is: Is everyone elses alternators completely silent? Or is a small amount of whine normal? Other cars I've owned have had zero alternator noise (Corvette, Firebird...etc) but all of them probably have lower power consumption needs.

 

[j91z28d1]

so my yukon doesn't have an alternator. I know, weird hybrid things. but I have also had many gm vehicles and none of the alts made any noise unless battery terminals needed cleaning, and that was more thru the aftermarket radio than under hood.

I do have one of these ungraded gm hairbrush alternators from our trucks swapped onto my c6. these are oem take offs on ebay for 100$. they are direct swap for your truck too, and they are 220amp rating and have more diodes to charge great at idle. I have a DC amp clamp and have seen over a 100 amps at idle with everything on, even with under drive crank pulley spinning it slower. not a single bit of whine from it.

I know you've already tried one new alt, but if it was a auto parts store, you never know what you get and this is a cheap upgrade as well.

the part number you can Google or ebay search is 13536552.

they look like this one. which is the most normal looking one to me. ebay listing's sometimes tag tons of part numbers so there's also a 180amp Delco that's not as good to me that they list sometimes too. it's has different electronics and a one way clutched pulley. no clue why.

 

[Doubeleive]

your problem is ground/power related and doing the big3 confirms that (reduced whine)
usually "audio" whine is because a power and or ground is not isolated enough or a power & ground are too close to each other or something is exposed that shouldn't be
so you might have a exposed wire, pinched wire, a hidden worn spot on a harness, etc.
it could even be a internal fault in the radio or amp.
aftermarket equipment CAN cause it depending on how it was installed (wiring wise)
anything aftermarket installed? fog lights? led/hid headlights, light bar or ANY other equipment?
if so disconnect it and see if anything changes
you can also try and isolate the issue by pulling fuses one at a time for anything not mandatory (lights on the dash won't hurt you) and see if the noise goes away if it does then you know it is due to that system somewhere

i can pretty much assure you it is not due to how the alternator is mounted nor the belt, type size grooves or any other nonsense.
also since you went thru 3 different alternators it's not that either.

basically you are chasing a ground issue or something not insulated properly from other wires/electrical system
best course of action is to probably try what I noted above pull a fuse for something and see if it goes away then go thru each one that you can without causing a drive ability issue.
a good tech with a oscilloscope could probably find it within a couple hours as the whine you hear is a specific electrical signal and will produce a visible waveform

Here are some possible causes of an audible whine and how they might appear on an oscilloscope:

• Power supply noise: This often appears as a low-frequency hum or buzz. On the oscilloscope, you'll see a continuous, low-amplitude wave.
• Switching power supply ripple: This can cause a higher-frequency whine. The oscilloscope will show a series of sharp peaks or spikes superimposed on the DC voltage.
• Ground loops:These can introduce noise that sounds like a buzz or hum. On the oscilloscope, you'll see a random, fluctuating signal.
  
  
• Interference from nearby devices: Electromagnetic interference (EMI) from other electronic devices can cause a variety of noises. The oscilloscope waveform will depend on the specific type of interference
  
  
  
• To identify the specific signal causing the whine, you'll need to:
  
  1. Isolate the source: Try disconnecting different components or devices to see if the whine changes or disappears.
  2. Adjust the oscilloscope settings: Experiment with different timebases and voltage scales to get a clear view of the waveform.
  3. Analyze the waveform: Look for patterns, frequencies, and amplitudes that match the characteristics of the noise you're hearing.