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Discussion Starter #1
Sounds like there is a pulsating propeller spinning under my TJ, '01 4.0, and it primarily sounds that way when I'm not giving it gas, regardless of being in neutral or not, in 2 Hi. When I give it gas, the sound is more like a constant grind I guess. Neither sound is horribly loud, but it's getting louder. In 4 hi it seemed to make more noise, think it might be in the transfer case? Don't really see any leaks, but I haven't checked the transfer case fluid (bought August 2013). All 4 brakes seem to be fine and unrelated to noise. It has shuddered a couple times, but not consistently, at low speeds. The U-joints on the drive shafts look well fitted. This thing makes so many noises but this one seems to be in the last few months.

Appreciate any help, even if it's to tell me I'm a hypochondriac!
 

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My first thought is to check if your fan is making contact with your fan shroud. Perhaps you have a worn trans or engine mount and depending on the load being placed, perhaps there is a slight shift that is making contact. You can easily enough check for wear on the inside of the shroud and/or loose fan shroud bolts.
 

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Discussion Starter #3
I don't see any issue with either of those things. I'm still pretty convinced it's the transfer case, in which case, I probably need to visit a mechanic anyway.
 

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Discussion Starter #4
OK, so I finally just jacked up the rear and ran it up to 45 and verified that the sound is coming from the rear. Something is grinding, shuddering as it slows down in neutral, and still sounds like a propeller. This colder weather seems to have aggravated the noise. The u-joints have no play, I'm kinda confused still in my limited experience. Hopefully I can do the same thing with my wife tomorrow so I can look under (safely to the side) while it's in drive.
 

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Discussion Starter #5
In conclusion, in case anyone Googles this, the rear diff was chewing up a gear, set bad or something. Expensive...
 

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In conclusion, in case anyone Googles this, the rear diff was chewing up a gear, set bad or something. Expensive...
do you have a limited slip rear end
 

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Discussion Starter #7
No, it's an open differential. I just went to a mechanic, partly since I live in an apartment with no garage, partly because it's freezing, and partly because I have no free weekends for a while... and partly because I really don't want to screw it up and had really reached the end of my very limited experience in diagnosis.
 
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