2000 Ford Taurus v6 3.0 not dohv. Started having engine knock when cold and under load, appeared to improve when warms up. Changed plugs, wires and tried higher octane but with no improvement. Online posts say maybe a bearing or anti knock sensor. Not sure if this engine has such a sensor. Really puzzling cause other than this the car runs fine. I am concerned if left will cause problems that I can't afford to fix. Please help.

since i owned the car (6 years) the engine knocks. i took car in 3 different times for repair, ford doesn't know why it knocks. they told me to use higher rated gas! i have 110000 miles now and it still knocks.