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Discussion Starter #1
I upgraded from 3.21 to 4.56 gears two weeks ago. I started hearing a very high pitched whine between 45 and 65mph only while accelerating. After that I no longer hear it. It almost sounds like alternator whine. With the windows up you can barely hear it and really have to listen. In fact if an older tech was in the seat, they may not hear it. If your driving where there are buildings on both sides, with the windows down, you can hear it better. I can't determine if it's front or rear of the Jeep.

Everything I read and listen to doesn't say gears. That is more of a low howl and mostly on deceleration. While they replaced the gears they replaced the axle bearings. So it could probably be that but i'm also wondering if it might be a u-joint going. Since the axle is now spinning a bit faster. The Jeep has 62000 miles on it. The 500 mile check up is on Saturday but this noise is driving me nuts (wondering what it could be, not the noise itself)

2015 JKU
6-Speed
33" tires, 2.5 inch lift.
 

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If the change happened after you got your gears done, then it is most likely the gears. Too much coincidence. When you are accelerating you are putting a load on them so they will make more noise.

Sounds like you are having them checked in a few days anyway. Did you get pics of the gear marking patterns, and the backlash numbers?
 

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Discussion Starter #3
I didn't as i dropped the Jeep off to have them done. I'm sure they have them written down for their records but I don't believe I got a copy. I'll have to look at my invoice.

Seemed coincidental to me as well. When doing any research all I found was decel noise or acceleration noise that sounds nothing like this.
 

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Take it back to the shop. Sounds like an issue with the gear work, based on the information in your post. Improper set up, bad bearing, etc.
 

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Discussion Starter #5
Yup, going in Saturday. I let them know when I made the appointment that I had a little noise. Luckily I work from home and don't drive much. I'm not super concerned like I said you really have to listen and since I just had them done, i'm probably a bit more sensitive to it. It's a good offroad shop so I know they will make it right. They do tons of gears.
 

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Hopefully they will get it sorted out for you.
On a side note, how do you like the 4:56 gears with the manual and 33’s.
What size are you running? I have 285 75 17 measuring a true 33.
 

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Discussion Starter #7
It's way better than the 3.21 I had but probably a bit too deep for 33's in my opinion. You rev out of first and second super quick. It works but I think they will work best with 35s.

So I may have actually found my whine by accident. I stopped at the mail box yesterday and when I got out, I still heard it. Not loud but same pitch. When I pulled into the driveway and popped the hood I think I narrowed it down to the alternator. I'll get confirmation tomorrow from the shop but that might be the issue and not the gears. Fingers crossed.
 

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It's way better than the 3.21 I had but probably a bit too deep for 33's in my opinion. You rev out of first and second super quick. It works but I think they will work best with 35s.

So I may have actually found my whine by accident. I stopped at the mail box yesterday and when I got out, I still heard it. Not loud but same pitch. When I pulled into the driveway and popped the hood I think I narrowed it down to the alternator. I'll get confirmation tomorrow from the shop but that might be the issue and not the gears. Fingers crossed.
I had a noise that I thought was an alternator going bad and it turned out to be the serpentine belt. It would whine and screech. One day I splashed a little water on the belt and the sound stopped. As soon as the water dried the sound came back. Installed a new belt and problem solved. Much cheaper than a new alternator to boot.
 

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I upgraded from 3.21 to 4.56 gears two weeks ago. I started hearing a very high pitched whine between 45 and 65mph only while accelerating. After that I no longer hear it. It almost sounds like alternator whine. With the windows up you can barely hear it and really have to listen. In fact if an older tech was in the seat, they may not hear it. If your driving where there are buildings on both sides, with the windows down, you can hear it better. I can't determine if it's front or rear of the Jeep.

Everything I read and listen to doesn't say gears. That is more of a low howl and mostly on deceleration. While they replaced the gears they replaced the axle bearings. So it could probably be that but i'm also wondering if it might be a u-joint going. Since the axle is now spinning a bit faster. The Jeep has 62000 miles on it. The 500 mile check up is on Saturday but this noise is driving me nuts (wondering what it could be, not the noise itself)

2015 JKU
6-Speed
33" tires, 2.5 inch lift.
A high pitched whine under acceleration.......I would suspect pinion bearing. Unless it changes pitch when you shift gears. If it does that it could be an idler bearing, alternator bearing, or something with the serpentine belt (engine related).
 

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Incorrect backlash
 

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Discussion Starter #11
Total coincidence. It's either my alternator or idler pullies. When I started the jeep yesterday, parked it was making the noise louder than it did before and I had a CEL of low/high beam high circuit which people mention is the alternator starting to go. This is now the second time this month I got it. I have my inspection this Saturday, going to have them test it.
 

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Total coincidence. It's either my alternator or idler pullies. When I started the jeep yesterday, parked it was making the noise louder than it did before and I had a CEL of low/high beam high circuit which people mention is the alternator starting to go. This is now the second time this month I got it. I have my inspection this Saturday, going to have them test it.
This is my bad idler pulley:

 
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