for as long as i owned my b7 when i would go to fill up which normally was around the time the gas light would come on, pressure sound would be there when i would take the cap off to fill. I recently put a new gas cap and Purge valve on. I now hear no Hiss sound at all. Is this normal or should i be looking for a small leak i dont drive enough during the summer to really know quickly if my mpg has change.