dammit! stupid seat. that's what it was for me too. like a million times. we always think its the most complicated problem involving bottom brackets and tapers and its as simple as right under our dumb-lazy-assses.

check your bottombracket/cranks anyhow. take it all apart and get to know it. its fun

as for your bars: tighten stem in both places then if still creaking - have fun with the headset!