I understand that a BB is a pair of bearings seated in a tube that is part of the frame, in my case aluminium.
On assembly in the factory I would think that the bearings are inserted dry as I assume that the profit margin
is reliant on thousands of bikes being assembled per day.
I believe that the outer part of the bearing moves in its dry metal seat and that what makes it creak.
Jan 2014 I bought a Cannondale Quick 4 that after a while would creak when I stood on the pedals going uphill.
I turned the bike upside-down and removed the screw that held a cable guide which allowed me to dribble about
ten drips of oil into this crank area then replaced the screw. I laid the bike on its side for an hour then again on its
other side to allow the oil to creep around the bearing seat.
I'm not saying this cures all creaks but in the last 12 months I haven't had a single creak.
Just wish I could say the same for my knees.
Cheers
Paul G