Looking for advice and info for a problem I have with my 2007 cts 3.6l with 95,000 km. Had it in for service last year and they updated the code in the computer for the timing chains. The last number of months it has made a slight rattle sound on startup, but went away very quickly. Also seemed to sometimes idle a little rough, but seemed to run ok. I suspected the timing chains, but assumed the dealer would not do anything about them until a code came up. About three weeks ago, got a code P0027. About the same time, noticed a sound like a knock or rattle when excelerating around 4000 rpm. Checked the oil, and noticed it was down over a quart. Never had to add oil before, and I change oil on or before oil warning. Changed oil and filter, and found non magnetic metal pieces on outside of filter. After changing oil, took it to the dealer and they indicated chains are worn, and replaced them under an extended warranty. After I got the car back, noticed the knock was now there at idle when warmed up. Took it back and dealer mechanic had a quick listen, and thought it was bottom end of motor. Dealer now wants $600 to remove engine to see if that is the problem. The rest of the engine is out of warranty, so if I have them remove it, would either get it back in pieces, pay another $600 to put it back together the way it is, or pay up to $9000.00 for a new engine. My theory is that the loose chains may have hit the covers somewhere, sending aluminum into the oil. At some point, a journal oil passageway has become pluged or restricted, and took out the bearing. I have no proof of this, but what bothers me, is if it is a rod, what happed to it? Is the issue with the timing chains possibly related to the knock? My son usually drives this car, it is his car, but under my name to save insurance costs. He bought car used with 47,000 km on it, and really likes it. He probably will be buying several vehicles throughout his lifetime, but very unlikely it will be another Cadi. I have used this forum in the past to find info, etc. and find it really helpful. Thanks for the responses.