Most likely, what you are hearing is "normal", given the nature of AUTO hubs.

As you climb a hill, you are able to load/unload the tires. It is this unloading that unlocks the hubs (why you back up to unlock). But, you are still driving, so what happens is when the tires get traction again, and you are accelerating, the hubs slam into the locked position again. Not a good noise and definitely not a good thing if you are trying to rock it out of a spot.

Either live with it until they grenade and then replace with manuals, or just replace them with manuals now.

Good Luck,
Michael