Sorry, should of said.
For my upper back, which is where the problem is i'm doing one-arm dumbbell rows, dumbbell shrugs, chinups, and variations on the chinups.
On average I'm doing about 3 sets of 10 reps of each
it might be that the ligaments holding the vertabrates in line are a little lose..
or the vertebrates rotate slightly during the exercises making that cracking sound