Help - Rear end hum - replaced carrier - still humming

[chrissurfr]

4Runner family,

I’ve had a humming sound coming from the rear of my truck for a while now - at least 10miles. I’m now at 19k miles. The truck is still under warranty and has been taken to the dealer to fix multiple times but they can’t figure it out.

I live in Houston so the truck has been through high water (bottom of doors) a couple times.

Characteristics of the metallic hum:
1. Happens around 30mph upon coasting or deceleration
2. If coasting, the sound remains constant but seems to get louder when slowing down to about 25mph - below or above that speed there is no noise
3. Seems louder in the cold
4. The sound only happens if under load and not with wheels in the air

What has been checked/changed attempting to fix:
1. Dealer checked and said it’s not wheel bearings
2. Rear dif carrier was just replaced under warranty - humming remains
3. I installed a clamshell bushing to get rid of needle bearing - that didn’t fix it

I’m out of ideas at this point and the dealer really isn’t much help.

what else could it be?
1. axles?
2. Some other bearings not in the carrier?

Thank you!


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[Teamoatmealpie]

usually its the diff needle bearing, which you have already replaced with the bushing.

Mine was on the front, most noticeable coasting under 40.

 

[chrissurfr]

Bump...anyone?


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[tristero]

If you replaced the diff, I would look at the driveshaft, joints, and rear axle.

 

[Jivewalker]

Tire noise possibly? Dust shield on brakes rubbing? Dry U joint? One of the pully's under the hood? Brake shoe dragging? Just some thoughts. Mine has a hum also that I can't figure out. I've given up and just accepted and listened to it for the last 40k, nothing broke yet. I'm at 186k though.

 

[chrissurfr]

Ok - some progress.

I lowered the truck about 1/2-3/4 of an inch and the vibration is much less.

Now knowing this, I think it is driveline angle related.

I'm probably lifted about 2.5-2.75 inches up front.

Do I need to get a diff drop to possibly fix this or do I need to reset the pinion angle?

 

[DigitalRJH]

That's interesting. I know with lifted Cherokees, the originals, not these new ones, that lifting them too high caused all kinds of vibrations and drive line angle issues that were not good.

 

[Mutant138]

I'm probably lifted about 2.5-2.75 inches up front.

Do I need to get a diff drop to possibly fix this or do I need to reset the pinion angle?

Do you know for sure or are you just guessing? I would try to get some measurement and compare them with other peoples lifts. I'm at 2.5" up front and it's pretty mild of a change TBH.

Diff drops are almost worthless on these trucks. Won't achieve much.

If I had to guess you where sitting at a 3-4" of lift and you are straining the driveshaft.

Figure out how much lift you actually have.

 

[Jetboy]

You may have a CV that's got a bad bearing inside it or something related to the CV. You didn't mention if it went away in 4x4 or not.

Possible bearings could be anything from wheel bearings to any of the bearings in the transmission or transfer case or drive shafts. Usually you can run it on a lift and use a mechanic's stethoscope to isolate noises and find which bearing it is.

 

[Grug556]

Could you have mild resonating from exhaust onto a close part or hanger and it acts as a music generator.