If this is your first attempt at making it quiet, I have a strong feeling you are using the Zalman 92mm fan too at the lowest setting using fanmate (which is 5v by the way). I also done this with my first experience and noise went down about half. Then I replaced it with a Panaflo 80mm L1A and also replaced my PSU stock fan with a Panaflo @ 7v. I changed all my fans to panaflo @5v and the system is not just quiet, its inaudible with a few other mods of fine tuning.
My tip for you is to replace the Zalman fan as they are much noisier than the Panaflo @ 5v. Even @7v the Panaflo is much quieter. The Intel stock fan is noisy at 12v (whines like crazy), but if you use the Zalman fanmate and set it at the lowest setting you will notice its much quieter than the Zalman fan @ 5v. But Panaflo fans are the quietest I have come across.
Any fan is fairly quiet @ 5v except, yes you guessed it the Zalman.. Well to me anyway.
As you do the above, the next source of noise is probably come from your stock fan in your PSU which is drowning out some of the other noises.
Good luck on future mods, you will notice silence is almost reachable.
Update: If you don't want to change any of your fans, your first step is to undervolt all your case fans to a low voltage (I recommend 5 volts). Just make sure the tempertures remain okay. Anyway you got a large 120mm fan which pushes a lot of cfm, so undervolting it won't be much of a problem with concerns of low airflow.