I fixed an extreme creak recently in my MTB (by extreme I mean ppl 20 paces away were looking back ). After several vists the the LBS where they _claimed_ to have swapped the cranks and BB with no result, I bought a BB tool and opened it. Inside the BB there was a fine brown powder, like rust ground up, that looked mighty suspicious to me, so I cleaned out the BB by squirting in WD40 until it washed all the cr@p out. Then I reassembled the BB with grease everywhere, even between the cartridge bearing interfaces and the spindle and housing, put it back in and now the bike has been quiet for 2 weeks, the first time in months. I also greased the crank bolts, both the thread and the flange, as well as the square taper. (I did that before to try and cure it with no result.)

I fail to see why the bolts must not be greased? The changing of the torque argument, perhaps? Or self-loosening?