Weird Hum when accelerating. Anyone have experience with this?

H20JNKY

H20JNKY

Member
So, I have this weird hum/whine and I can’t tell if it’s coming from the engine bay or drive train. I replaced both idler pulleys, because one was bad and thought the other was causing the weird hum, but the noise is there. No weird noise while engine is on and parked.

When I step on the gas the noise increases with acceleration, as soon as I take my foot off the gas it disappears. I’m thinking maybe rear pinion bearing, but wouldn’t it make the noise even if I was coasting? This noise is driving me nuts!

Jeep drives great!

Thanks for the help!


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Definitely sounds like a differential bearing from what you're describing. First check that all driveshaft yokes are tight as well. If you jack up the Jeep and put it on jackstands, have a helper drive the vehicle while it's in the air while you listen with a stethoscope. It will be obvious as you check the gearboxes and wheel ends if a bearing is bad. Make sure your helper is someone you can trust.
 
WJCO said:
Definitely sounds like a differential bearing from what you're describing. First check that all driveshaft yokes are tight as well. If you jack up the Jeep and put it on jackstands, have a helper drive the vehicle while it's in the air while you listen with a stethoscope. It will be obvious as you check the gearboxes and wheel ends if a bearing is bad. Make sure your helper is someone you can trust.
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I kind of did that this morning, jacked the back end up and put in drive and tried to replicate the sound. But I was in the Jeep. I like your plan better. Will do that this afternoon.

Here is a video of the sound: https://youtu.be/E-q5G-EBCpA


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Hard to say for sure from the clip but being that you only hear it on acceleration, I would have to guess it has something to do with your gears.
 
wayoflife said:
Hard to say for sure from the clip but being that you only hear it on acceleration, I would have to guess it has something to do with your gears.
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I’m going to check that there is no play in the drive shaft then remove dif cover and see if I see anything. Not sure what to look for but I’m sure I will notice something, if this is the problem area.


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I will add to those in the gear related camp. I had a similar issue when not fully torquing my pinion nut. Once I tightened it back it was fine for years.
I had replaced my pinion seal, tj d35, and miscounted threads.
 
Ok, so I went and took the dif cover off! Now, I don’t want to dis the local Jeep club down here in Carmen, MX but I’m really pissed on how they put my cover back on. About 6 months ago they replaced my driver side axle shaft. When I went to take the cover off today, there were 2 bolts broken that had been RTV’d to look as though they were screwed in!!! One of the studs I was able to get out and the other one needs to be drilled out! And to really add insult to injury, the dif was bone dry! I’m pissed at them and myself for not checking.

Anyway, here is the video of the gears with the dif cover off. They seem to be okay, however I think my passenger side axle is bent and rubbing. Can that be causing the noise? https://youtu.be/fUePD46_pEw


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Well, no oil in your differential certainly could be the cause of your “weird hum when accelerating.” [emoji23]
 
Take lots of pictures and make that shop pay for it. Chances are your bearings are shot now. Disregard that axle noise for now, may be Normal or may be slightly bent flange.
 
fiend said:
Well, no oil in your differential certainly could be the cause of your “weird hum when accelerating.” [emoji23]
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Yep, I’m thought that as well when I took it off.[emoji23] I put the cover back on and will wait until the Morning before I fill it, and then test drive it.


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WJCO said:
Take lots of pictures and make that shop pay for it. Chances are your bearings are shot now. Disregard that axle noise for now, may be Normal or may be slightly bent flange.
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I’ll try, but this is deep into México....like 100 miles to Guatemala deep! Lol. I may be forced to have the local Jeep dealership fix it for me. Which is probably a much safer bet.


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I had that same hum when my rear diff sprung a leak and I didn't notice. It only hummed on acceleration. Once I filled up the diff, the humming remained. I drove it that way for a long time like that with no problems.
 
H20JNKY said:
Ok, so I went and took the dif cover off! Now, I don’t want to dis the local Jeep club down here in Carmen, MX but I’m really pissed on how they put my cover back on. About 6 months ago they replaced my driver side axle shaft. When I went to take the cover off today, there were 2 bolts broken that had been RTV’d to look as though they were screwed in!!! One of the studs I was able to get out and the other one needs to be drilled out! And to really add insult to injury, the dif was bone dry! I’m pissed at them and myself for not checking.

Anyway, here is the video of the gears with the dif cover off. They seem to be okay, however I think my passenger side axle is bent and rubbing. Can that be causing the noise? https://youtu.be/fUePD46_pEw
Click to expand...

Well damn, that really sucks! While the gears might be okay, you're bearings may not be. More than likely, the source of your sound.
 
H20JNKY said:
Ok, so I was able to put a camera and shoot some video. Certainly sounds like gears. Could it be my boot? It’s torn, I don’t think so, but thought I would ask. Here is the vid: https://youtu.be/Tcoi5isfvHE
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Sorry to say it but it sounds like it's coming from your gears. More than likely, you have something like a pinion bearing that's going out but really, that's just a best guess.
 
wayoflife said:
Sorry to say it but it sounds like it's coming from your gears. More than likely, you have something like a pinion bearing that's going out but really, that's just a best guess.
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If it’s the pinion bearing, or any one thing, do you have to swap all the bearings, seals and gears? Or just the problem part? Thanks for the help!


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H20JNKY said:
If it’s the pinion bearing, or any one thing, do you have to swap all the bearings, seals and gears? Or just the problem part? Thanks for the help!


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Click to expand...

Honestly, being that you were running for as long as you had without any fluid in the diff, I would replace the pinion and carrier bearings just to be safe. You'd get all that with an overhaul kit.
 
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