What kind of cranks?

What kind of BB?

Have you checked your pedals?

Have you checked your saddle/seatpost/bars?

Have you inspected your frame for cracks?

All of those things could cause creaking, but if you found play in the cranks, then I'd put my money on that. Any way you slice it, in a battle between cranks and BB, the BB will win. Steel is tougher than aluminum. So I'd say your cranks are shot. Until you get new ones, I'd just tighten the hell out of it and try not to crank too much.