when ever i do a longish run , few miles or so my filler cap pops ? like a pop pop pop pop sound , anyone else notised this ? also when i go to clean around where the filler cap i see fuel mix ( or what i belive is fuel ) with water , i mean whan i spray uner the arch it leaves a water with a fuel stream down my drive , ok i may have some over spill now and then , but every time i clean the car ? should i worry about it been a fuel leak ?

Don't worry about the popping as it's due to the vacuum inside the fuel tank. They are vented but there's still quite a strong vacuum as when you use the fuel in the tank air has to replace the space if that makes sense. I filled my car up again yesterday as I hadn't since I did a longish drive to Bristol visiting family, took the filler cap off and there was quite a vacuum holding it in lol.

As far as the possible leak goes you may have a leak from the tube which goes down to the fuel tank, but then again if there were a fuel leak even that bad it probably wouldn't pop because the vacuum wouldn't be as bad. Best advice I can give you that side of things is to have a look underneath the car when you haven't washed it to see if you can trace any leaks. It's probably not a fuel leak as even a slight one you'd smell it probably even inside the car and definitely when it's parked up. Plus you'd notice a decrease in fuel economy but then again it depends where it's leaking from.