That could be caused by air (or trapped air), in the coolant. Air would normally be purged after a couple heat up and cool down cycles. When the coolant gets hot it expands, and whatever that is at the top of the radiator (where any air would normally collect), gets purged out and sent to the radiator overflow. When the radiator cools down and the coolant shrinks, it draws back in from the overflow tank, which would draw in coolant from the bottom of the overflow tank. Thus after a couple of cycles, normally air is purged from the system.
If you have a blown head gasket, hot combustion air from the cylinder can be forced into the coolant. This overpressurizes the coolant, causes overheating of the engine, and excess air continually in the coolant. A shop can check for this with a compression test on the cylinders, to see if they all have the right pressure, or one of the cylinders is 'leaking' somewhere.
The problem with a headgasket problem, is that coolant can also leak into the cylinder, and ruin the engine, bearings, and exhaust. So you definitely want to have it fixed quickly IF you do have this problem.
I would suggest watching the amount of air in your radiator closely, to validate whether you have air in your radiator or it is always filled up to the top with coolant. I think you'll find you have air.