I worked for GM and there are good techs, and not so good techs, just like any shop....just a head's up to anyone going into any shop...ask the SM who his best engine/diagnostic guy is...if he says they are all good, repeat the question....then demand he works on your vehicle....one more thing, hate to say this, but it's true...if you are of the female persuation, have your boyfriend, husband, father, etc., go with you to do the talking....hate to say it, but females tend to get the short end of the stick.....
They should have heard the rattle on start up, and not wasted time on diagnosis....this problem kind of started on early 2000 Ecotec's...the problem back then was a restricted oil orifice, which did not allow the chain to get lubricated....the fix back then was replace the chain, tensioner, cam and crank sprockets, the orifice(larger opening), and if necessary, the guides.....
The rattle would progressively get worse, until the chain would break, and then you would have bent valves and other problems.....
In your case, at minimum, the chain and tensioner should be replaced, the rest inspected.....I'm sure there is a bulletin(TSB) out there for this problem....Just for ha-ha's, ask their S.M., if there was a tsb on this problem, by punching in the engine and codes set in a TSB search....also ask him to show you the labor op time for this job.....as I said before, there is diagnostic time, and part of the labor was used in taking the timing cover off.....this time should be subtracted from the labor op for the job......with that rattle present, there should have not been any more than 1 hour diagnostic's time.....their top engine/diagnostic guy should have picked this up......