You have to check all of your fans with the computer off. Open it up, stick your finger in between the fan blades on each fan and give in a manual spin with your finger staying in there. Be sure the space is clear of cables and everything else. Take the card out and do the same thing. When you install new stuff, you move things around that get crammed in fans sometimes. I had this happen after installing my last video card. It turned out that a motherboard power wire was lightly grazing the cooling fans on my radiator. Totally didn't think it was that, but it was.
After each time you check the system, power it on and listen. Then repeat until you find it.