A strong teen or old fart?

Aftermarket cpu fan.

I would think that the gpu fan would make that kind of noise, not the cpu fan.

Well, personally I wouldn't replace the fan on a 6850. It's just not worth the price and hassle. What I would do is add some case fans, and use a custom fan profile along with a gpu temperature monitoring software like GPU observer. Then I would lower the fan speeds at temperatures below 80C. What are your temps?

I'm talking about your GPU temps (GPU means graphics card). You can get this information by downloading a software called HWMonitor or a windows gadget called GPU observer.

A custom fan profile is a profile where you set up your GPU fan speed at different temperature intervals. You can do so with programs like MSI Afterburner.

Stock fans cpu get loud. Case fans can be bother some too when you are idling, check bios to adjust fan speed there.

I think is fine.

I never bothered with changing gpu heatsinks since the trouble & cost is not worthwhile for me. If gpu noise is really the root of evil than download msi afterburner and map your fanspeed %.

Well either way, you need to find out what makes the noise. Why change the cpu cooler without even checking if the noise is coming from the gpu?

Some case fans can be noisy, but at around 20db it's pretty much silent.

First determine which fan is causing the noise. Open up AMD Vision Control (a.k.a. CCC) and enable custom fan speed in the overdrive section. If you can get acceptable temps with low enough speed then download riva tuner and set up a custom fan profile there (forgot how it's done but anyway it's better than to have constant speed). If it's the CPU fan you can try to lower its speed in bios, but don't expect any miracles from AMD stock cooler. The alternatives are pretty cheap, tho, Xigmatek Loki for example is quiet and it's good for a moderate OC. If you think you need to replace the GPU cooler I recommend Arctic Cooling, I have their Accelero L2 Pro and it's exellent, however for 6850 you need something like Accelero Twin Turbo Pro. Tripple check the compatibility b4 you buy!

I am betting that is your CPU fan, get a coolermaster hyper 212+, just installed one yesterday on a phenom 955 and it is whisper quiet.