I had this just after I collected the car and it seemed to be coming from the passenger side exhaust triangle. I took the car back to the dealer and they said it's a common problem with EX's, but it will go on it's own after about 1000 miles ????
Great I thought, another dealer fob off - but it
did dissappear on it's own at about 600 miles

- very odd.
I had good look under the car at the time, but could not see/feel anything that was loose?
If was a known issue a year ago, perhaps the dealers know what it is now and have a fix.