I would add some more fans if possible. I run Zalman 120mm case fans and they are almost silent. Make sure you have good air flow. Tie all cables up and out of the way. add a fan to the front of the case if you don't have one already. Try to keep a couple of slots on the Mobo clear below the vid...
Did you put some arctic silver on the cpu before reseating the heat sink? If not take it off again and clean the cpu and heat sink and reinstall it with some arctic silver on it.