My cars head gasket recently went and my local garage reckons it because a heat sensor went on it. Its now been replaced But is it right that when you turn a valver off and its hot it makes quite a loud buzzin as the water pump stays on till its cooled down to a safe temp? bit like a turbo timer! mine still doiesnt do it and im worried! Does it happen to other valvers or is the mechanic a gimp?