They do all whoosh, but it is a known issue where the cap does not allow air into the tank once it runs lower. (Having pressure in the tank is normal due to controlling petrol vapour emissions - the whoosh should be release pressure, not letting air in due to a vacuum) One way to tell is if the bike runs better after releasing the cap, and runs worse with it on going for a while before releasing it. The vacuum builds up counteracts the pump trying to get petrol out. You can take the cap apart and make sure it is working ok - I have a diagram somewhere about how it works if you need it. Mine makes lots of noises it hot weather as the pressure in the tank is vented.
