Bet I know what it is.....
Take a look at the bottom of your blue orb and see if it is direct contact with the PCI slot adjacent to the AGP port. I put a blue orb on my GF2MX card and it was LOUD!!!!. I couldn't figure it out because it was fairly quiet outside the case.
I thought it was loose so I was looking around and that's how I found out it was contacting the PCI slot. I lapped the sides of the fins down a bit to provide clearance but I'm sure just pruning back those fins that are by the slot would fix the problem too.