cooling system air voids

I have a 2009 G6 GT 3.5 L. The cooling system appears to have air in it. When at idle and rev engine, I can hear water bubble or waterfall sound in dash as if the system has air in it. I took it to dealer and they did their best to eliminate all air, but I can still hear it. Also, the other night while driving the florida turnpike for about an hour at high speed, the temp gauge pegged hi all of a sudden. I turned on heat full blast and cold air was coming out. I got off highway and parked car. No evidence of coolant anywhere. I slowly burped the system by slowly opening the coolant cap on reserviour. Closed cap and started engine. Temp came down to normal and drove home. How do you properly vent this system? Anyone else have this problem? Any ideas will be appreciated! No evidence of coolant leakage at any time. Head gasket problem? Thanks