I have a little question about the spare wheel area in my mk4 astra. When I removed the wheel and the tool kit there is some wadding underneath like uinsulation in the form of a circle. Once thats lifted out there are 4 holes 3 of them have what looks like pressed discs in, and the last where 3 oclock would be is a rubber disc with a small hole in the middle to the outside of the car underneath. What is this for? I will get some pics soon. Thanks in advance for any help.