XPS 8960, noisy power supply

I have an XPS 8960 desktop with the Intel Core 9 processor. It appears to have a 750W power supply in it (although it is difficult to identify it via the Dell webpage). Right now it is making a rapid staccato clicking sound as if a fan blade could be hitting something. I was giving some thought to replacing the power supply because of that noise. But when I search the Dell parts I don't see a 750W power supply for an XPS 8960 that looks like the one in mine. I see a 1000W power supply that has a similar appearance to what I see at the back of my unit. I was wondering whether someone had ever changed the XPS 8960 power supply that came with the Core I9 CPU and knew whether to place it with the 1000W power supply (parts notes it is compatible with the 8950).