Quieting down my computer

I already have my q6600 watercooled, but long story short my brothers staying in my room now and I am forced to quiet down my computer. So I need some recommendations on how I can accomplish this. I have $300 and my computer needs to be almost silent, spec's are in my sig, Any idea's?

You say you are already running watercooled, but no mention in your sig identifies what exactly you currently use. Is it a pre-built kit? What size tubing? How big of a Rad? What fans?

Sorry I am using a Danger Den Black Ice Xtreme II 120.2 rad, 1/2" tygon tubing, 2 yate loons fans, d5 laing pump. I was thinking of adding my 9800gx2 and northbridge to my loop and get a pa120.2 to compensate for the extra heat, would this work?

Would the PA120.2 be in addition to the Black Ice, or, as a replacement? Also, how do you currently have your Rad mounted? Is it external or mounted to the bottom of the case?

It's in the bottom of my case, the PA120.2 would in addition and it would be mounted in the front drive bays

With that setup, you should have more than enough to cool a GPU/CPU and northbridge. I see you are running Yates for fans. Make sure you get the same fans for the PA Rad as well.

Also, you may want to add a fan controller so you can set the RPMs for each fan. Most Yates can run up to 1600RPM, and with your additional Rad you should be able to drop the fan speed down to 800RPM which should help reduce overall system noise. Very nice setup.

Is there a cheaper radiator that would work for my situation

Cheaper? Sure, you could always go with the Swiftech MCR220. Its one of the best bang for the buck Rads out, and it doesn't require high CFM fans in order to operate.

would that be sufficient for my loop

If you want to cool the quad as well as the gx2, the pa120.2 should be enough. That radiator is a very good one. Sell the other radiator to offset your cost. I went overkill and got a mcr220 (120x2) WITH the PA120.2. When I was cooling my e8400 at 4.15Ghz (1.46V) and the 9800gx2, I noticed that the temp with the addititional mcr220 was about 1-2 cooler underload than without it. And that was with my pa120.2 on the top of the case using case air temp to cool it. I am sure if you have the pa120.2 at the bottom sucking in cooler air from the bottom, it would be better. Trust me the Pa120.2 is a high performer, no real need to have it with another radiator.
If you decide to get the MCR220 with the attached reservoir (not sure if it is the same model number), then it is good in that you dont have to worry about have a reservoir and can attach it to the back 120 fan using the bracket. It is a decent performer with good air flow. By itself, it cools about 3-4C less than the pa120.2 underload with same fan settings (from my experience). So it all depends on how much cooler you want things.

but see the problem with that is the second cheaper rad is the would be a cheaper approach and would consume less of my time

Yeah in that case, get the MCR220 (MCR220-R QP under frozencpu's page). That is the one I have. By itself it performs slightly less than the pa120.2 but will get the job done. Also you can install in on the back where the 120mm case exhaust fan is. That way, save yourself time and trouble. By itself it will do a decent job of cooling both the quad core and the 9800gx2.

I intend on mounting the second radiator in the drive bays, that way it will be sucking in cool air through the radiator.