Because you do not indicate the model, I decided to just look at the troubleshooting section of the first Bosch microwave that came across. They write that the presence of steam, vapor or moisture is quite acceptable (page 21 of the [link|https://www.ovenmanuals.com/ge/jnm3163djbb/owners-manual/|General Electric JNM3163DJBB Owner's Manual|new_window=true] ). Perhaps there is nothing to worry about and if there are no other problems, it is not worth trying to fix the normal operation of the equipment.