I've replaced the axle bearings a while back in my 73 maverick and it eliminated the "grinding" sound and all was well until a few weeks ago. I'm hearing a grinding sound again. Could it be some other bearings? The fluid level is good. What's the best way to check?
You might try getting the car up in the air (jack stands under the rear axle, front tires blocked) and put the car in neutral. Try rotating the rear tires by hand and see if you notice anything. Maybe a warped brake drum. Odds are though that if it is an axle bearing that it is going to make noise under load/with weight on it. When is it making the noise? All the time? Just under acceleration? Turning one direction or the other? Does it go away under braking?
I jacked the rear end up and put it in neutral. Turned the tires by hand and the only thing I heard was a slight noise in the gears. like wore out bearings. A bumpy de bump sound. Not a warped brake drum sound. It very well could be one of the axle bearings gone bad. I just had both replaced about a year ago. I start hearing the sound when I get up to 5-10 mph and it continues at all speeds after. I also heard a slight "squeaking" noise when turning the rear tires. Sounded like it was coming from the differential. Like metal against rubber... What Th' ?