My bike makes a creaking sound when I push hard on the pedals...

I ride an Alu Tirreno Razza 2.0 (2006) with carbon seatstays...
I thought the creaking sound was coming from:
(1) The handle bars and or the stem -- got them changed and replaced at Performance (free of charge ). But still some creaking after that --though less.
(2) the seat post or the saddle. Got that checked out. Seatpost tightned. Still some creaking, though less.
(3) May be the pedals... got that thightned
......Still creaking when I push hard on the pedals (to go up a hill for example)

It's pretty annoying....any idea what it could be? The alu frame? A crack in the frame? Is it dangerous potentially?