i recently purchased a 76 300D. when i lift off the accelerator i get a whirling noise almost like the sound of a down shift as the motor begins to slow. the noise only occurs when i let off the accelerator and is proportionate to the speed i am traveling slower=quieter faster=louder. it occurs regardless of being cold or driven for 8 hours. the sounds seems to come from the differential area. Differential is full with clean fluid. is this sound normal for a differential with 460k? and what steps can i take to eliminate the noise.

 

Sounds like a gear mesh / wear issue.
460,000 miles!!
I not surprised its being to "object a little".
Stuart