Strange advice given how easy it is to remove and reinstall an external bearing crank. I'd suggest (assuming you have the tools and knowledge) to remove the crank and cups, check the bearings then grease everything as specified, and torque everything to spec. If the noise persists, go through LongIslandTom's list to eliminate other possibilities.

I say this because bottom brackets are so frequently the cause of the creaking noises especially those that only present themselves under power. If you were suspecting some other, less likely item that was difficult to test for (say a lugged joint in the frame) then it makes sense to look at everything else first. Similarly if you had already greased and torqued the bottom bracket twice already it would make sense to start looking elsewhere. For a first shot at the problem, might as well go right for the obvious suspect.