thekemist no offence but have you even got under you car to have a look?this is whats made toymods seem like a cyberspace garage,this has happened over the last few years.not a group of car lovers that have a go and then ask for advice etc.mate seriously its the piping etc hitting or one of the brackets!if you got under the car safely{jack it up and throw the spare tyre under the rail}and shake the system,im sure my 5 year old son could work out what is making it hit.
mick