coolant leak

Do you smell coolant or is there a visable drip? If yes the 3 most suspect spots are a small leak from the radiator itself, the heater control valve (which should be located close to the firewall) and the upper intake plenum/gaskets. If no the upper intake plenum/gaskets have coolant passages on both ends and could leak directly into the intake and burn off during the combustion process

Check your intake manifold it's a common thing