I'm having the same trouble. IT IS THE CRANK BOLTS. I tighten them down, they loosen up, I tighten them down, they loosen up...............
After I tighten them, no creaking.
I was thinking of going back to the bolts from the old BB. They're tightened with a 14mm socket. There was never any creaking with the old BB with these bolts.
The new BB, Interloc Racing, has 8mm hex key bolts with rubber seals. I have a suspicion that the rubber seals may have something to do with the loosening. Before I put the old bolts back on I'll remove the rubber seals on the new hex bolts and see if that solves the problem.