Have had this Terrain about a year and half..I went thru the Update software to fix key problems with Nav System..I mentioned something to the Mgr that my Terrain was starting to knock and sound funny..Got this answer"Oh well thats typical for a 4 cylinder Terrain..Are there any engine updates or fixes for this problem?? I really have not pursued this problem..Sometimes I hear nothing and other times it sounds really bad like ballbearings in a can..Thats about the best way to describe it upon acceleration..Any help would be appreciated..Thanks :help: