Whirring noise after alternator change

I have developed a whirring noise after replacing my alternator in my 09 Tahoe LTZ. It goes away in neutral and park, and after acceleration, but gets a bit louder when a load is placed on the electrical system(lights, heater, a/c) when in drive or reverse and brake on(idling at stop sign with foot on brake). Is there a noise filter or some other electric component I may have blown when changing the alternator; I followed all the precautions like disconnecting the battery neg terminal. The belt is like new and I’ve changed the alternator twice with the same remanufactured model from Advance Auto. The noise was not there with the original alternator which I replaced because it was overcharging.

Sounds like a baring that increases enough for you to hear when under a load. Do you hear it thru your speakers or just from under the hood?

It’s not through the radio speakers at all, and is less audible when I’m under the hood because of all the other engine noises, but it is there. The first replacement alternator had a somewhat rough pulley so I exchanged it for one with a nice smooth pulley, but the noise is still there, maybe even a bit more. The belt looks very good, and I’d hate to get a new belt to try if there is some electrical solution. I find it hard to believe I got another bad alternator! I can’t believe Advance could sell these if they were that faculty.

Ok, I would not guess that you would get 2 bad alternator in a row. Take the belt off and see if the noise is still there when running. If it stops, it could be the belt or something being caused by both likely good alternators. There could be a ground problem that all these rigs seem to have a weak spot for. The only thing that is constant is the belt and that you changed an alternator.

how did you determine it was overcharging? how old is your battery? have you checked and cleaned your battery cables and grounds?

ive had the other pulleys suddenly go bad after doing a job like yours countless times. that or the tensioner isnt applying the same force as it used to. when you take the belt off in above suggested diagnostics prior to starting it physically check all other pulleys. spin them by hand and check for shaft play.

Took the belt off and the whirring went away. Tried a brand new belt and noise still there-no difference. Then checked the tensioner and idler and both had a tiny bit of play, but not enough for me to feel it’s those. They both turned smoothly. Wouldn’t they be noisy no matter what the rpm is? The whirring only occurs between about 500 and 900 rpm, then goes away with higher revs. Took the second reman’d Car Quest alternator back and Advance mgr felt so bad, he gave me a brand NEW Car Quest unit. Guess what, same noise! And still sounds like it’s coming from the alternator...using my ears of course. The Advance mgr also verified he heard it, and was perplexed. So, would you get an alternator from a different source and ask for a refund, or, replace the idler and or tensioner and then ask for a Delco or some other brand if the idler or tensioner don’t eliminate the noise? This is getting old!

idler and tensioner they may spin smoothly but they could be dry. also there should be little to no play in idler and tensioner pulleys. make sure you get the whole tensioner not just the pulley if thats an option. also under idle is generally when there is the most slack in the belt. under higher rpms the engine is pulling on the belt harder and can potentially make the sound go away as it adds extra pressure to a pulley.

A bad pulley bearing can spin smoothly by hand with no noise until the belt tension is added and the load on that belt while running does cause a noise. I always grabbed the pulley and pressured it and moved it to FEEL some roughness.

Can you do a video of the noise and post that?

Okay, I’ll try to make a deal with Advance on an idler and tensioner, on the condition that if those don’t give me a remedy, they refund the alternator and I go a different route. They DID try to help with the brand new alternator, but it’s no solution if all CarQuest alternators are junk.