I also have a Mustang that does the same guys, even at the lowest throttle opening, ( especially late at night when its quiet) u hear a ticking sound. When u open up the throttle more, it gets muffled by engine noise but it is still there.Altho at no throttle opening, the ticking stops. I at one point assumed that it might have been a stuck piston, or gunk that it was hitting every time it made a revolution. But in order for that to be true, the ticking sound would have to increase with the engine speed, and its notright? Steady quick ticking sound. Yea quite the head scratcher. Anybody else with this problem? 
