@ram1009: Doesn't the fan on the heatsink make noise? I definitely hear the sound coming from the stock heatsink.
He's simply being technical. The heatsink is the chunk of metal, which typically has a fan bolted to it. I haven't used a lot of noctua products, but I believe they focus on low noise cooling products. Coolermaster is pretty good as well.
I don't know if they still make passive heatsinks (no fan), but they did exist in the past, they were expensive and had very thin copper sheets which fanned out like pages of a book. Those may not be capable of keeping up with modern CPU's though.
Other potential sources of noise:
Mechanical HDDs (SSDs don't make noise)