Loud metal on metal is generally not a good thing. The 12 o'clock, 6 o'clock wiggle, like you said, might be a good indication if you have some bad bearing in the knuckle pivot or on the spindle with the wheel bearings. It could be either or both if you get more than 1/16" of wiggle.
Another possiblity is that the leaf spring may be busted or the shock blown and it's going through the travel until it either bottoms the shackle against the frame...BANG!...or maybe the bump stop is making the noise.
Just some ideas. Good luck tracking it down.