Originally Posted by rhusak
Sorry to hear of your issues..
I would be much more inclined to look at the rear axle.. Those kind of noises are indicative of a pinion bearing or ring and pinion issues.. Check the axle grease asap!
Seems more like a rear axle, (aka: differential), noise.
My differential has been humming loudly, (not howling), for 13 years,
(105 k miles), anytime the the accelerator is applied
However, since the OP hears a "howl" when he "lets up on the accelerator or when it is coasting" he might have a different problem.
'96 Safari, 132k miles