Is anybody here an expert in diagnosing axle noises?

2 weeks ago mine suddenly started making a rhymic growling noise at low speeds. It was brought on by slow cornering or acceleration, but vanished if I lifted the pedal, and disappeared above 40 mph.

It was definitely axle speed rather than prop shaft or gearbox. I eliminated wheel bearings by swapping over complete half shafts with another good axle, and cleaned up the brakes and fitted new handbrake shoes. So it appeared to be localised in the diff/crown wheel and pinion region.

I tried changing the oil, just in hope, and noticed that there was a slight leak from the pinion seal, but not enough to have caused any significant loss - the oil was right up to the level plug before I drained it.

Over the last week the noise has slowly diminished, and today has virtually vanished, apart from a slight hum at about 20 mph if I touch the accelerator.

I was all prepared to do a complete axle swap, having a good spare lined up ready, but now I am wondering whether it has, miraculously, managed to cure itself. It's as if the new oil is encouraging it to "run-in" , so I am tempted to leave it and wait and see. I don't relish the job, although having just extricated the spare from another vehicle I can see the tricks now to avoid unnecessary dismantling (eg leave the brake calipers and pipes behind but swap the handbrake cables)

Has anyone any experience or suggestions?
Thanks.