I will add to the other things mentioned as things to look for. Other causes of this is aluminum vs. steel. The two metals have different expansion rates and when they do this "creaking" has been known to occur. Very common with alu. frames. Another possibility is the crank arms need a little grease on them when you put them on the b.b. spindle. Another possibility is the threads on your pedals need grease when screwing them into the crank arms. Another possibility is the threads on the b.b. cups need grease when installing it into the b.b. shell. Other than the above mentioned checks that is all I can offer.