What is optimal airflow directions?

[BehindEnemyLines]

I need help with my case cooling. I've one front fan, one left side fan, and the PSU (no exhaust fan from back). Please ignore the airflow direction from the picture, as they don't fully apply to my current setup.

Here's a picture of the fan placements.

Numbers show current airflow (see picture):
(1) Exhaust is only from the PSU. There's no secondary exhaust fan from the back.
(2) Exhaust from inside case to the outside (left side fan from the bottom of the case).
(3) Intake from front of case (front fan).

Should I make fan number 2 be an intake fan instead? If I do that, can I just remove the front fan since my computer doesn't run too hot (Althon 550MHz w/ two 5400RPM HD and a Chaintech TNT2 - The AGP Chaintech doesn't have a fan, it relies on the front fan to push cold air across its heatsink). What concerns me is that the computer is on most of the day and during the night for video encoding.

From the current situation, what is the best cooling setup? I don't have an exhaust fan under the PSU (there's no cut out for it).

To minimize noise, what is the best cooling to noise ratio? The front fan is noisy w/ the side fan lesser. The PSU is the most quiet. And the CPU is noisy.

 

[sbw]

I guess I'm not sure what it is that you are trying to accomplish here. If your temps are fine are you want to quiet the thing I would try to replace that noisey psu fan along with swaping out case fans with something quieter.

 

[OulOat]

Bigger fans => less noise for cfm. Less fans = less noise. You can get a bigger heatsink that uses a larger quieter fan, and you'll probably cool the cpu better. Bigger quieter hsfs are cheap too. Your hds are probably fine without cooling, but just to be safe you could put a fan blowing air at them. HDs don't need that much airflow, just a constant low flow will work fine. That's why I recommend you getting 2 panaflos or NMBs, they are both silent and will keep your TNT and HDs cool. Just make sure the fans can get plenty of air, ie. nothing is impeding the flow of air.

Edit ---
If you are the handyman type, you can just do the 7V mod on your fans to quiet them down.