I would recommend taking the drum off to inspect the internals. Causes for brake grinding tend to be fairly easy to spot. A typical cause for a drum is excessive shoe liner wear which allows the rivets to touch the drum. Another cause I've seen was the liner actually crubling and falling apart allowing the metal to grind on the drum directly. Most of the liner was found at the bottom of the drum. The latter was likely the fault of a complete failure of the brake shoes. I believe it was a wagner pad. while such a failure could occur with any manufacturer's parts, I tend to stick to OE or quality name brand pads. In some cases, I use performance pads depending on the application.
It wouldn't hurt to replace some of the hardware as Lemon Crevice stated. I would add that you should check to make sure that the cylinders are not sticking either as it is possible that the brake may be engaging moderately with the brake off. This could cause premature wear and/or excess heat allowing the shoe to wear down to the metal or fail.
Ultimately though, you'll need to locate the root of the problem. Drums can be reasonably reliable, but need do tend to have more parts that can fail. Calipers by comparison do tend to be much simpler overall.
