2 answers from the following forum.
"The dealer after 3 trips determined it was air trapped in the radiator. all they did was let the car run for about 5 hours w/ the heater on and it got rid of the air bubbles, no more noise."
"We took it to the dealer and they finally solved the problem by "burping" the car. What was explained to me is that the unit is an "open" system vs. the closed system normally used for cooling and that an air pocket had somehow got trapped. They angled the car (varying side to side) and ran the heater for almost a full day and that seemed to fix it - noise has not returned."
http://www.automotiveforums.com/vbul...sloshing+sound