I'm having an issue with my gas tank not venting. I have seen plenty of posts explaining that a poor venting can cause a lot of running issues and my bike starts to miss in upper rpm's. I starting noticing that my gas cap would hiss and whistle when i shut off the bike and when I open the cap I would hear a gush of air. I checked the lines and none of them were pinched or blocked. I then removed the lines and took it for a ride and the tank still builds pressure and the gas cap whistles. Is this normal? Is there something else I should check?