Humming noise starts at 40mph

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For a few months now I have had a humming/howling noise whenever the Jeep hits 40mph on the dot. The sound increases with more speed but levels out at about 65mph and is then oscillating, changing between a little higher and then lower pitch every couple seconds. Almost like the A/c cycling on and off except much much louder and the sound is there whether the A/c is turned on or not.
Had a mechanic friend check it and he could not find anything wrong with the wheel bearings. Tires are worn a tiny bit unevenly because I had the same tires already before I changed out bad shocks/struts x4 this past spring. Noise was already there before suspension parts were changed out but has gotten much louder lately. Noise did not start when I first got the tires but later (they are stock size A/T tires and were initially very quiet even at high speeds). Tires have been rotated every 6,000 miles and another alignment was done a couple of weeks ago. That shop also said there was no problem with the wheel bearings and blamed the tires. But the noise is getting louder and louder. Shouldn't the tires wear more even now that the suspension is fixed? There is also considerable vibration in the steering wheel when driving on one particular road in my neighborhood but not others.
Any ideas??
 

Ksat

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Wheel bearings can feel tight but be failing nonetheless. Invest in a Chassis Ear, or a knock off of one, to help narrow down where it's coming from.
 

1Done&Home

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For a few months now I have had a humming/howling noise whenever the Jeep hits 40mph on the dot. The sound increases with more speed but levels out at about 65mph and is then oscillating, changing between a little higher and then lower pitch every couple seconds. Almost like the A/c cycling on and off except much much louder and the sound is there whether the A/c is turned on or not.
Had a mechanic friend check it and he could not find anything wrong with the wheel bearings. Tires are worn a tiny bit unevenly because I had the same tires already before I changed out bad shocks/struts x4 this past spring. Noise was already there before suspension parts were changed out but has gotten much louder lately. Noise did not start when I first got the tires but later (they are stock size A/T tires and were initially very quiet even at high speeds). Tires have been rotated every 6,000 miles and another alignment was done a couple of weeks ago. That shop also said there was no problem with the wheel bearings and blamed the tires. But the noise is getting louder and louder. Shouldn't the tires wear more even now that the suspension is fixed? There is also considerable vibration in the steering wheel when driving on one particular road in my neighborhood but not others.
Any ideas??
Do you have cross bars on your luggage rack? My bride confirmed my hearing a humroar that increased as speed increased. I installed a wind deflector and now the noise is gone. That’s all I got.
 

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1Done&Home

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These are a few pictures in my garage.( with my faithful assistant )
 

Weazerdogg

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Having exact same issue. Was always a low hum which I assumed was tires but starting this January has gotten slightly louder, same thing, starts about 35-40, gradually increases in volume until about 50-55 then levels off and kinda "goes away" with other noises at that speed but if you "hunt" for it it's still there. Have had all 4 wheels off the ground, all the wheel bearings are solid. I actually bought one thinking it was the case but never swapped it out due to both fronts being solid. My tires are almost worn, getting new in Fall, hopefully sound changes or goes away so I can narrow it down to tires. But will be watching this thread.
 
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Thanks for all the suggestions!
Don't have a roof rack, so it's not a wind noise.
Was considering new tires because nothing else seemed to have changed to create that noise. Would have been a shame since they are only 20% worn.
An out-of-the-box thinking mechanic suggested flipping the tires on the rims and see if it makes a difference. I was able to have that done for free, so I did. And the noise changed! Didn't go away fully because the tires are still worn uneven. But the feathering that used to be on the inside is now on the outside. The sound is much more like I am used to for AT tires and doesn't oscillate and whine anymore.
I will look into the pinion gear as well! Based on 282k mileage on my KJ, things could well be wearing out.
 
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tommudd

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Tires could very well be it
Sounds like first you have an alignment issue
Next , the tires, once they set up a wear pattern nothing is going to change that and will continue to wear in that direction, just nature of tires
Also with that amount of miles, suspension is shot unless it has been replaced ( new springs and shocks ) letting the poor little KJ sit way lower than stock height . This allows the alignment to be off and to wear the tires more
On level ground , measure left front, middle of the wheel ( hub area ) to bottom of the flare and report back . Ive had them in my garage that were 1.5 inches lower than stock height
 
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Suspension has been replaced twice - most recently this past spring. Including front UCA & LBJ. After new struts and shocks all 4 tires had 19" from center of wheel to fender. Right now, after a few months, the front still has 19" but the rear is at 18.75" and 18.5". I am thinking the rear springs may also be worn out?
Have not replaced them as I don't have faith in me using the compression tool.
I was told during the last alignment a few weeks ago that it was very difficult to get everything to within acceptable numbers because the frame is not perfectly square. This vehicle has never been in any accident, not even a fender bender. I did run over a load of firewood on a mountain road last year, nowhere to go except off the cliff so the wheels took a hard impact. I was expecting to have a flat tire but luckily not. Two other vehicles were stopped less than a mile down the road with flats. It seemed that the noise got noticeable after that event. Tires are in good shape overall according to tire shop. No separation or other issues.
 

tommudd

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First you do not need to use a spring compressor to install new rear springs , especially stock ones
After removing shocks and jacking up more they literally fall back in easy
Next if you ran into / over a load of firewood then the cradle got of shoved back on one side
Go find a really good alignment shop and have them check it out since the old shop does not seem to know what they are doing
 
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That is good to know about no compression tool needed. I may tackle that replacement after all.

Finding an honest shop is a struggle where I am. The alignment shop I visited is the highest rated one in town. And actually did not try to upsell me on a bunch of things that were not broken or not needed, which was almost shocking given the way other businesses do business around here.
What would be the repair to the cradle if it was pushed back and misaligned? It's a good guess as the right front wheel took more of the impact. The firewood did not hit the underside of the Jeep, only the tires made contact. How much work would it take to straighten it?
 

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