ive got an 04 plate 172 and when its cold ie just started its fine but if its warm and im sitting at a stand still i can hear a fait tapping sound if i rev the engine it picks up and sort of becaomes a more constant noise not tap but then when back to idle it tapps again, my father told me its nothing to worry about but the car is my pride and joy and i want to keep it in as good cond as poss so does anyone know what this could e and how to get rid of it?