Now I expect it is just me, but why does my engine sound different now the car has done 7500 miles?    When I say sound different, what I mean is when driving at 55-60MPH the engine seems to sound slightly noisier than it did a while ago.. not real noisy, but sounds slightly louder as if it needs to change up gear, even though the revs are normal, around 1700-1800 rpm....   It has not just started it has been like it a while :(   Also, I think I know the answer to this, whilst sitting at t