I didn't assume anything, I just wanted to point this out to clarify that fan noise isn't just about the card itself. As for proof, there are lots of sites (Tom's Hardware, Anandtech, etc) that compare different brands of cards by noise level—search for reviews of whatever card you're looking at and you're likely to find a chart comparing them. I've also personally experienced some rather large differences by switching brands of the same card, with both AMD and Nvidia.