Please help I've been trying so hard to stop this noise but my mechanic told me there's isn't much we can do. I find it so annoying and loud. We've changed two aftermarket alternators and at the end I went to the dealership and bought a Acdelco one but it still didn't stop it. From all 3 alternators 2 of them made the same noises. Any tips and advice will help so much. Thank you

video of the sound attached here
https://imgur.com/a/m76IiVT

 

its a hummer h2 2003

 

I'm thinking that if the sound does not change swapping between 3 different alternators, then the sound is likely not coming from the alternator. As with many who come here with mechanical issues and questions, I'd suggest checking on one of the many GM truck or SUV forums as those use the exact same drivetrain and are far more common so more likely to find answers from someone who has had the same issue.

 

have they checked the water pump or fan clutch or the tension pulleys or if the belts are worn or if the harmonic balancer is separating. maybe something out of alignment on the drivetrain?

 

Ever hear of a Mechanics Stethoscope?
Did you try running without belt installed?
Do you know how many pulleys are on the front of the 6.0?

 

“From all 3 alternators 2 of them made the same noises.”

So, which one did not make the noise? Are you saying one was not noisy or different noisy?

Was the AC Delco rebuilt or brand new?

You sure it is not the fan clutch or something near the alternator like a pulley or glazed fanbelt?

 

Idler pulley has a worn bearing.

 

Like everyone else said...if you tried 3 different alternators then it's not the alternator making the sound. It could be so many things. One time I had a leaking hose, the fluid got on the belt and made my H2 sound like I had a bird living under the hood. Fixing the leak and adding a new belt got rid of the noise