Hello, I have problems with the pressure conditions in my fuel tank. When opening the tank cover, especially with full tank, I hear a long hissing/sucking, sometimes even bubbles rise and after long journeys at high speed a cracking/relaxing of the tank. Have once attached an image of the tank ventilation. How the system is ventilated is so half understandable to me, but how or what does the ventilation work, so that no vacuum arises?