Loud PC-Help me quiet it down!

What CPU and motherboard do you have? Some motherboards can control the CPU fan speed based on the CPU temp. The Zalman cooler should have also come with a FanMate speed controller. Are you using it? Do your case fans plug directly into the PSU, or do they plug into the motherboard?

That makes it easier if all the fans plug into the motherboard. You can use a fan controller in that case. I don't know how much you're looking to spend or where you live, so I'll post newegg links.

ZALMAN MFC1 Plus-B Black 6 Channel Multi Fan Controller - Retail $36.99

You could also just buy a few of these if you want to do it on the cheap:

ZALMAN FAN MATE 2 Fan Controller - Retail $4.99

Another option would be to replace the case fans with low RPM fans.

Scythe SY1225SL12M 120mm "Slipstream" Case Fan - Retail $8.99

Scythe S-FLEX SFF80A 80mm Case Fan - Retail $13.99

www.silentpcreview.com is a good resource.

Yes it could. The simplest solution is to listen to where the noise is coming from, popping off the side cover works wonders to helping you to locate the noise, just be sure to not unplug the fans on the side cover while the computer is on, or better yet disconect them while the computer is off and unplug. And than run the comp with the cover off and listen to where the noise is coming from.

While your in there you mine as well pull out a can of compressed air and give the computer a thorough cleaning. I have an 8800gts myself and that dual slot cooler on it can conceal quite a bit of dust so hit it with the compressed air inside the fan cooler to knock it out (while the machine is off of course). With any luck that may have been the problem with the dust blocking the exhaust port and preventing it to cool properly so it spins up to 100% speed and thus alot of noise. If not go back to plan B) Locate said noise.