[rotorwrench]

The 55 should still have the old Ford rear axle used basically from 1949 to 56. Does it whine under load or only when you coast? The pinion bearings may be worn or there is a loss of preload if it whines when coasting. If it whines under load then the gears are most likely shot.

At least it has a third member that can be removed and worked with on the bench but finding parts can be a bear.