I have a 2000 explorer sport 4.0 ohv and.....when in park there is an annoying clattering sound. I took it in to one mechanic and he said i should hurry and get it to the Ford dealership....Is it time to trade in...or can it be fixed for a reasonable cost and what is making it do that?! It doesn't "knock" or "clatter" in other gears, just while it is in park idling. Any ideas?