burping noises in hose

i have a 99 alero with v6, i would run the engine till it warms up, it runs a little hot, between the 1/2 and 3/4 marks every once in a while it would get a little higher. when i fill the thermostat openes up the hose under the air intake makes a burping or surging noise and i can see the hose throbbing. i was giving the engine a little gas and watching the overflow tank which i filled up and air bubbles would come up. i dont know if its air in the system or not, the fans do come on. i havent seen coolant in the oil or vise verse. the engine runs fine. every other day i have to put water in the overflow tank. the only water leaks i have seen is water coming out of the overflow hose.