mine just got louder, i am going to check if anything looks different. i just read on another forum that it could be due to a torn cv.
" the fact that sound starts when you let off the accelerator can most likely be an attribute of a loose part loosing centrifugal force, perhaps something like a cv boot or something along those lines has vibrated itself loose. when the torque is released from it, the wheels instantly begin to slow down, this might be when it is happening... "
this was for a newer car though. mine is 15 years old which is why i am skeptical of my own problem, although it does have a torn cv boot, which i will try to replace. we'll se what happens.
based on the fact that noone with the actual same symptoms have followed up, my guess is that this is a life ender.