It was my turn to take the car into Renault today and have the problem checked out. They just called (even though I wanted an answer at lunchtime!) and said it was a problem with the mid section of the exhaust. Theyve ordered the part and now Im waiting for it to arrive and have it fitted.
We know that this is a very common problem with the 172. A question to anyone who had this problem and subsequently had it rectified on their car - has the rattle/buzz ever returned?