It is probably the water level that is low. In the morning before you leave open the radiator cap and check the water level.
Never check when it is hot. Very bad idea.
I had an issue with a BMW almost exactly the same age and model. Took BMW forever to fix it and when they did figure out what the problem was they charged me like R1200 to replace a single water pipe. Apparently because they had to move half the engine to get to it. I can't see how bad design on their part is my problem