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short rattle on startup is your timing chain tensioner... they clag up around the oil inlet, happens when the motor only gets used when cold regularly and doesnt get a chance to warm up, run some engine oil flush thru for about 5 changes every 5 thousand k's... pretty common problem with alloytecs
whenever the oil drops its temperate and gets thicker again... its like trying to fit diff oil thru a straw... happens slowly till ti warms up.
but mainly is present first thing in the morning... these engines arent pretty when you take the front cover off after 80,000+ k's, carbon build up galore for some reason