There is a thread on the forum regarding a "brief rattle noise on startup " on ecotec engines.Some have thought it was oil filter related.This is wrong.Its a timing chain tensioner issue. There have been numerous tensioner revisions for ecotecs and the latest revision (since about 2009) finally corrects the rattle which is actually a loose chain on startup.Check your tensioner and if the head of it is FLAT then you have an old style. The new one has a raised bump on the head.A few seconds of looseness every time you start will eventually lead to a stretched chain and failure down the road. My vehicle is a 2006 and had one of the older versions which I changed out.There are instructions for doing the change out but BEWARE----the plunger of the old tensioner may spring out when you unscrew it from the block so hold that plunger somehow. Mine sprung out and fell down inside the engine.
I was able to get the parts out with a magnet luckily so beware.
I was able to get the parts out with a magnet luckily so beware.