So, after months of thinking my annoying creaking sound (only when standing and climbing) was coming from my SRAM Force crank/bottom bracket area, I think I've finally figured it out.
I switched to some new wheels, and guess what? No more creak. I'm now thinking it's coming from the front or rear hub (I haven't had time to figure out if it's the front or rear yet).
So, what causes creaks in hubs and what can I do about it? The wheels are Easton Orion II and the hubs are Easton's "R-series with patented Twin-Thread Technology. Gray annodized finish. Precision-sealed cartridge bearings with asymmetrical, low-drag seals."