Scirocco Register

Yep, can't say I've noticed it when driving but when I park up and turn off I can hear it for about 10-15 seconds and the car hasn't really rocked around enough to cause the amount of noise if makes. Its the original cap so I'll have a look and see if if it's any good.

Tried out the cap valve, it does work but not very well it seems to take a lot of pressure for it to open, the tank would have to be under a fair bit of vacuum for it to release and once open it doesn't close immediately either. I'd say there would be enough vacuum in the tank to pull fuel back down the hose before the cap starts to vent.