X2 on it likely being a bad u-joint on the left or right axle shaft. Spraying the u-joint with a lubricant like PB Blaster etc. would only serve as a temporary possible confirmation of the bad u-joint. Even if spraying the u-joint works to eliminate the squeek, consider that a short-lived temporary fix until the offending u-joint can be replaced.
A superb direct-replacement u-joint upgrade for the Spicer 5-297x the factory installed would be the stronger & more durable Spicer 5-760x.
__________________ When you have a choice, buy American.
Worst case scenario would be the ujoint breaking and taking out axle shafts with it. Driving on pavement that is less likely, It would be in an off roading situation I would worry about the breaking being possible.