My 2000 Subaru Impreza has started making a weird kind of screeching noise for a few seconds when I clutch in to start it then goes away. Runs perfect other than that and is only a recent thing and doesn\'t do it all the time. I have been told it is the cambelt that needs changing?? Its done 188,000km so is due for its next one? How much is this or what else could this noise be?