93 altima bubbling

The coolant reservoir bubbles when the car is running. It starts the moment the car even starts to warm up a little. The radiator cap is brand new. The thermostat is not that old either. once the car warms up the valve cover feels really hot and I'm worried because I know it has aluminum heads and I don't want any damage to it. does anyone have any ideas. I've been told a few things but I'm not sure where to start. Any help would be greatly appreciated. THANK YOU!!!