Yeah, unfortunately I've had the same thing and it was PSU for me.
It's worth bypassing that part of your loop with some extra tubing (if you can) and then slapping the stock coolers on...or even pulling the 1 card from the loop and leaving the other. If you are careful, you won't have to drain your loop and would only lose a few drops of water.
Again...slow and steady.
Good luck- keep us posted.