Can you help with diagnosing a whirling noise?

JONCHEROKEE2002

MEMBER
2002 JEEP GRAND CHEROKEE
150,000 MILES

The Whirling noise isn't audible until about 30mph (except if you are looking to hear it) it gets a little louder as the car goes faster.

The sound reminds me of 3 things
An electric motor being spun up. (Though not as high pitch)
A little like tire on pavement.
A little like gearing down in a standard (transmission) when going slightly to fast for that gear.
(but a consistent pitch)

The Jeep rides rough, so I suspect the struts or shocks are "worn"

There are a few leaks I've noticed. But all fluid levels are fine, and clean enough. But just to be detailed, the leaks are in/near the transmission as well as the struts.

I first thought it would be the tires because worn struts can do that, but the tires seem evenly worn enough, with only a slight increased wear on the outside 3/4 inch.

Any expertise will save me a week in diagnosing, thanks a lot.

7 Replies

FIXITMR

MECHANIC
9,990 POSTS

Could be wheel bearing.

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Wednesday, March 21st, 2012 AT 11:14 PM

CARADIODOC

MECHANIC
33,873 POSTS

Noisy wheel bearings sound like an airplane engine and are real common. To be sure you find the correct one, run it in gear when all four wheels are off the ground, then listen next to each one with a stethoscope. You'll hear the difference.

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Thursday, March 22nd, 2012 AT 2:27 AM

JONCHEROKEE2002

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3 POSTS

Got to look at the noise while she was on a frame hoist, and its definitely coming from the front differential. So I am going to replace the bearings. If I have a professional do it, how long should it take them to replace all 4? (2 carrier, and 2 pinion)

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Sunday, March 25th, 2012 AT 3:48 PM

CARADIODOC

MECHANIC
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Boy, are you going to be disappointed. Before you replace the wrong parts, unbolt the front drive shaft, then drive the vehicle. You'll still hear the noise with no load on the differential. If you still think it's the differential, remove the half shafts and find some old outer cv joint housings to bolt in to hold the bearings together, then drive it again and you WILL still hear the noise. The front differential won't even be turning.

It is normal to hear all kinds of noises from a differential when you're standing next to it. Listen to the rear one when it's running on a hoist.

There's two better ways to prove a front wheel bearing is noisy. The first is to run it in gear on the hoist, then listen next to each one with a stethoscope. One will be making a little noise, but the other one will be obviously much louder. You won't hear it by just standing next to it because there's no weight on it. The second way is to use a "Chassis Ear". That is a tool with six microphones, a receiver box, and headphones. You clip the microphones to suspect parts, then switch between them and listen while driving. The noisy bearing will be real apparent. Be aware that many mechanics don't even know about this tool but all new car dealers have them and they're used regularly by suspension and alignment specialists. You might be able to find one at an auto parts store that rents or borrows tools. The old model uses microphones that need to have wires run inside to the switch box. The newer model uses two like that but has four wireless microphones.

Noisy bearings are an extremely common problem on all brands of vehicles that use this bolt-on style bearing. You shouldn't even be looking at the differential because that is just going to be misleading. Those bearings can get noisy but that is not common.

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Sunday, March 25th, 2012 AT 5:56 PM