Did you figure out what the problem was? I have the same problem although noise (howling) seems to be coming from middle of engine compartment. Doesn't matter if car is in neutral with engine off (coasting) noise is the same, most pronounced at 45 mph but evident from 30 mph on up. I replaced left front wheel bearing but that didn't help. Boy was that a treat! That thing was froze in its mounting hole something terrible! (I had only intended to remove it to test the bearing but by the time I got it out it was shot.) I haven't started on right side yet as I'm am starting suspect transmission.
1999 Taurus AX4N transmission
