I would guess it is the interface because there is enough evidence in this thread to support it. The bolt wasn't that tight when you checked it (and they should always be checked after the maiden voyage and 2nd and 3rd depending on length). You said you didn't tighten it that tight in the first place so I would guess it is the crank-spindle interface. Let us know how it goes, but I bet it is gone on your next ride.

In the shop of today, ticking and creaking noises almost always comes from the BB threads. The outboard bearings rock more I think and when they get some grit between the cup and the face or don't have enough grease they begin creaking. I have found that this is inevitable for high mileage riders.