1999 Dodge RAM 1500: Strange noise, need help ID'ing

I have a 1999 Dodge RAM 1500 with about 70k miles on it, 4WD.
Recently it started making strange noise. The most typical way to make the noise is to start braking from higher speed and slow down to about
20-30 MPH.
It is hard to say where the noise comes from. It also appears if I just coast at that speed range. Sometimes there is more of it, and sometimes less.
The noise frequency is proportional to speed, if I slow down, the frequency goes down also. It is rare to appear below 20 MPH.
I will be happy to do more experimenting and report my findings if necessary, I am worried about it.
i
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All noises are clues. No noise is good. All noises are bad. Some noises are very expensive to resolve and others are very inexpensive. If you want help, please do better to explain the kind of noise. Where it is coming from and what you and the vehicle are doing when they occur. Steve

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down the engine(Do not lock the column) also be aware no power brakes. Put the trans. in neutral as well.
Roy
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Yes, I feel vibration with my feet.
i
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Okay, stop me if I have it wrong. You have a vibration felt at your feet with the engine shut off and coasting. If so, take a look at your rear tires/wheels. Spin them up see what you have. If nothing is found when on the machine. Then rotate the tires front to back. Let's see if the vibration moves or stay's the same.
Roy
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How many miles on the tires? Does the vibration lessen on curves? Do you notice it under acceleration? Are your windows closed tight?
Roy
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I feel vibration (higher frequency than engine running) when the engine is running.
I tried today (for a brief moment, did not have enough time) to reproduce the noise and then shift transmission to neutral. That seems to lessen the noise. I will redo my tests more carefully if you think it is worthwhile.

I will check, I think that my front wheels are original (70k) and rear wheels are much newer, but I could be wrong and maybe all my tires are not that old.

It seems to lessen on acceleration.
Opening windows does not make me hear more of the noise.
i
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Get somewhere so you can try it in different modes.

Have you been under the truck to check u joints and for loose exhaust? If not do so. If all is well I'd go back to the rear tire's and wheels

Sometimes a partially open window can create a sound.
Roy

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The noise is definitely coming from the rear, I had our nanny and my wife stand outside as I drove by. It sounds like a bad bearing noise, I recalled my experience with a 5 hp single phase Baldor motor that I fixed by replacing bearings, it sounded very similar.
Any more ideas? maybe I can apply some grease with a grease gun, somewhere?
i
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wrote:

one pressed on.
Roy
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Thanks! How can I tell if it is the axle bearings, differential, or u-joint? I want to do some diagnostics.
i
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wrote:

loose.
Roy
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Will do tonight.
i
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How full is the differential? Is the lubricant level where it's supposed to be?
--
Budd Cochran

John 3:16-17, Ephesians 2:8-9, Romans 3:23, 6:23
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I will check that tonight.
i
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