HELP! Humming noise in Jeep,

[mcolford]

So while driving my Jeep, I have noticed that when I let off the accelerator (usually 30mph or over) I will hear a humming noise. The noise is NOT there at all while on the accelerator, but is there when OFF the accelerator. I am completely stumped. Anyone got any ideas?

I know my way around an engine bay.. But this is just weird to me.

2002 Jeep Grand Cherokee 4.0L auto trans 4WD.

 

[ASD]

Lifted with oversized tires? Some times tire hum is easier to hear when off the throttle. Also those jeeps suffer from death wobble even when lifted just a tad.

 

[Mackey]

I was going to suggest tire noise as well. If you rotate your tire and notice a change you'll know that was it.
But it's not that bad. Now you've got a Hummer and a Jeep.

 

[Glock22]

Sounds like a bearing somewhere in the drivetrain,under acceleration it keeps things tight enough you don't hear it. When you let off that enables things,like bearings to rattle. Check your u-joints in your drive shaft.

 

[IN71vet]

Tires probably forgot the words to "Hit the Road Jack."

 

[vitamink]

Does the noise vary relative to speed? Get on the street and turn while accelerating or decreasing speed. If it gets worse while swerving left or right it's a wheel bearing. It could also be a tire going out of balance from losing a weight or chunk if rubber which is common in large chunky tires

 

[GLOCKMAN23C]

I had this issue with my '99 grand. I bet you have a bearing in the rear end that is shot, under accel the bearing is loaded, when you let off the loading goes away allowing the bearing to change position allowing it to make noise. If it is one of the outer bearings, on the rear, they are a pain/ or / expensive to replace.you may check the inside of the rear tires for leaking fluid, that may give you an indication of which side bearing has failed.

 

[darkkevin]

probably a pinion bearing in the diff., front or rear, probably rear. dana 35 diff's love to eat pinion bearings.

 

[mcolford]

I dont notice the sound as much when its cold (the Jeep, not the temp outside)..... Not lifted. Stock.

 

[halfmileharry]

Sounds like a bearing somewhere in the drivetrain,under acceleration it keeps things tight enough you don't hear it. When you let off that enables things,like bearings to rattle. Check your u-joints in your drive shaft.

Without hearing it my self I'll say to check this...I'd definitely check fluid levels in the drive train as well. Notorious gaskets leaking on differential covers and yolk seals.

 

[Bigtanker]

Easy fix. Just don't ever take your foot off the throttle. Problem solved.

 

[sht4brnz]

See if the noise disappears if you place the vehicle in neutral while you are hearing it.
Have you ever heard the noise at idle while the vehicle is stopped?

If not gear related: rear end,
Check for vacuum leaks around any and all plastic diaphragms/vacuum line junction and vacuum test the brake booster.
Have it smoke tested. 11 years of heat cycles makes plastic brittle and won't always be obvious to spot a failure.

 

[phylodog]

Had something similar in my 05 Wrangler, had the rear differential gears replaced under warranty.

 

[cavskillz]

Sounds like rear end noise to me as well, checking fluid or replacing would be a cheap start. See if some lucus quiets it down.

 

[steveh_131]

agree with the above who said it was bearings in your rear diff.

had to rebuild my rear dana 35

 

[d.kaufman]

Its a pinion bearing In the rear differential. 99.999% positive. Been working on cars for over 30 years

 

[halfmileharry]

Its a pinion bearing In the rear differential. 99.999% positive. Been working on cars for over 30 years

4x4 can be a front as well. I've had to do both in my Grand Cherokee.

 

[Mosinguy]

Check u-joints. Dad had the exact same issue on his 02 Explorer. Everything was fine until you let off the gas and then there was a hum in the cab.

 

[mcolford]

Hum occurs in neutral as well while moving. Not present when stopped. Sounds front to me, so tomorrow morning Im going to run up to the garage and crawl under it and check the mentioned fluids, and possibly replace them. Then go from there.

 

[halfmileharry]

Hum occurs in neutral as well while moving. Not present when stopped. Sounds front to me, so tomorrow morning Im going to run up to the garage and crawl under it and check the mentioned fluids, and possibly replace them. Then go from there.

It's not a bad job to rebuild the differential on those if you can set up the gears. The rest is a piece of cake. Cost around $380 is what it cost me. I put a complete used front assembly in my older ones for $200 but the 2002 will be double that at least and you still have the same common problem waiting to happen. Hope you get by with fluid but I'm guessing 90/10 you won't. Then again I'm not there to hear it first hand. Crossing my fingers for you.