Once and I while I here this sound from the rad, more from the cap itself. The car runs cool all the time. I did an anti freez test and the coolant is good. Do I need a new thermostat or a coolant flush???

 

Replace the radiator cap. It's probably not keeping pressure. Matt

 

yeah my mom had a car do that, then it dumped dex-cool all over a wall-mart parking lot. Then some dude with ****** put it back on loose so it didn't blow a hole in the cooling system from too much pressure I was inside when the guy did it and we dumped more coolant at McDonald's. By the time we could get a new cap we put in 3 gallons of coolant and water.

 

If it's when the car is hot, then it's just not holding pressure probably. Need a new cap.
If it's when the car is cold, then it's normal bc the radiator is sucking the coolant back from the overflow by using the vacuuim relief valve on the cap.

 

My car did that lately and I found the problem was a leak at the water pump because of those assy oem hose clamps. I replaced all my clamps with the screw teeth kind and that did it.