It does sounds like the U joint making that noise.
As you can hear it when the shaft is under load and the noise goes away when in neutral.
To check the U joint remove the driveshaft and move the U joint in all direction look for hard spots or too much play.
You will also see a rust colored powder if the U joint has failed and needs replacement.
This is due to metal on metal contact without any lubrication. That also creates noise.
Here are couple of helpful articles:
Please let me know of any questions.
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Monday, September 13th, 2021 AT 8:54 AM