RobCrezz :
Dont worry about it, some of them occasionally do that. You can try moving the pipes and radiator around just to move the air bubbles.
I did the same Nzxt Kraken G10 set up with an AMD HD7950. At the time I purchased the bracket, they had a star * next to the HD7950 indicating some boards were manufactured with a low gpu chip set in the die box and needed a shim. Yeah, so it was. The shim needed thermal grease on both sides and slid around in the die box. It needed just the right amount because too little took the temps past 100c. Whoa.
And the beginning of this month (Jun '14), the HD7950 was no longer on the Kraken G-10 compatibility list. Oh, oh. The kit needed 4 post bushings so I used 11/32 grommets and I had to remove the foam block off the back bracket because it wobbled. But when it was finally corrected, I had to trace down a bios update for the motherboard and the vrm/mosfets needed heatsinks. Going through that much of problem.. . the high peak temps came down 20c. It's clocked 1.2ghz from 925mhz and like your GTX 680, appears to have room for more.
And now, this gurgle. Uhmm. If it's harmless, it's weird. It sound soothing like an aquarium water pump and also like the bathroom sink. Makes me think of brushing my teeth. I suppose I could RMA it. I can't move the hoses. How's it going with yours?