Hooray, fixed bottom bracket creak

[Dan B]

Turned out to be quite simple: the BB had worked loose inside the shell. But I'm wondering what the root cause may have been - never having had one come loose before, is it more likely that I did a rubbish job installing it in the first place (about a month or so ago), or is the BB shell thread maybe in a bad state (the frame is steel, 1980s) or is there some other likely cause?

(For context, bog-standard square taper cartridge BB, fixed gear bike)

 

[lpretro1]

Those type of bbs need to be done up pretty tight so if you didn't have a torque wrench to do so it may have been not tight enough