Bad U joint or 4WD problem?

[Clyde Frog]

In 4HI today cruising around at about 20 MPH, I noticed this "helicopter" type sound and that my Jeep just overall isn't sounding right. The noise definitely doesn't sound like it's coming from the rear so I'm hoping it's a bad U joint and not something wrong with my 4WD system.

Have a listen and let me know what you think:

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The sound isn't occurring in 2WD or when I coast in 4HI. Only seems to happen when I accelerate in 4HI.

 

[yellocoyote]

Check the rear boot on your front driveshaft for cracks, rips, etc. The noises you describe are the same as what my failing DS sounded like when it went. I could only hear it in 4WD as well.

You may just need to replace the CV end, but I would get underneath and check it out first. The condition of the boot is usually a very good indicator.

 

[Clyde Frog]

Is it safe to guess that a likely cause was my dad having spun my tires in 4LO during the last storm? There was a little bit of a "pop" sound that he said he thought was just the Flowmaster.