So this morning I start up my '05 ST w/ 2.3L Duratec and notice a strange noise coming from the engine - very loud. It seems to be coming from the valve cover area and is a loud metallic ticking - almost like a bad lifter in an OHV engine. The car has given me zero problems and I change my oil every 3K using Mobil 1 5W20. The car seems to run fine, not running hot just the loud tick. The car has almost 50K on it so the warranty has definitely expired. Any ideas on what could be the cause?