I've got a 12-bolt GM axle from an 81 Chevy installed in my 50 Chevy truck. Lately I've noticed a pretty good howl/whine when I let off the throttle/coast. Accelerate, and the noise goes away.

The noise seems loudest around the trans, but notice my rear axle pinion seal is leaking, which could indicate a bad pinion bearing. I replaced the pinion seal before I installed the axle, and was careful to install the nut in the same position (number of turns) as before removal.

Is the noise more likely to be from the rear axle than the trans? I would think if it was the trans I would hear it under all conditions, not just coasting. Obviously I have a pinion seal issue at a minimum but was wondering if I need to be looking at the trans as well.

Thanks in advance.

Joe.