What type of BB do you have? I've never had a square taper BB creak but BB30... well, that's another story.

On a different tack, I once cured an annoying but mysterious creak by putting some light oil ("3 in 1 oil") onto the chainring bolts and leaving it lying down in the sunshine. I think the oil got right in there due to the different expansion rates of the alloy chainrings and the steel chainring bolts.

Hope you get this sorted.