2003 Ford Taurus 24V DOHC Clacking

I own a 2003 Taurus with the Duratec 24V DOHC engine. I am having and intermittent problem with a clacking noise that seems to be coming out the exhaust or near the head although I cannot pinpoint the problem. It almost sounds to me like a manifold leak although the mechanic cannot duplicate the problem. This noise only happens upon initial acceleration after the car has just been started and only persists for a minute or so until some heat comes off the engine. It will not do it at idle, only under acceleration. It will do this on occassion with a warm engine if it has sat for a bit (not completely cool) and is restarted. It never does it while running or after warm up. Secondly, I am getting some knocking when I go uphill, nothing severe, but knocking nonetheless when the car is under load so to speak. Also, sometimes it seems the auto choke is on for no reason. I'll put the car in park and it will be revving at 1200-1300 RPM. Idle is between 7-800 when in gear.