creaky crank/bb

Hi

Recently ive been experiancing a creaking/clicking noise as I cycle my
mountain bike. Adjusting the Bottom Bracket bearings seemed to fix this for
a few weeks then it would reappear. I decided to buy a sealed cartridge to
replace the factory fitted bearings, this was OK for a while but I am now
experiancing the same problems.

The creaking noise seems to occur when I apply force to the pedals, so it
happens twice a revolution. It usually occurs when going uphill but also
happens after freewheeling down a gradient, when I start pedalling to to
continue my speed as the momentum runs out. It only only occurs when
pedaling.

The only thing I can think it could be is the crank arms moving on the
tapered squares, but this all seems pretty well tightened?

Any Ideas would be appreciated as its a tad annoying and noisey!