This is the same vehicle that was referenced in the oil filter thread: https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4809623/all/Sludged_filter For those who didn't see that thread in the oil filter section here is the situation: This is a 2010 Cobalt with the 2.2L ecotec. He has owned the vehicle for about 5 years now and up until a few weeks ago the oil has apparently never been changed. We had originally thought a family member had filled it with Amsoil a few years back, but after further investigation...the oil had actually never been changed. The dipstick had only clumped sludge with no oil reading. So we changed it and here was the resulting cartridge filter: The bottom of the filter housing had about an inch of standing sludge, that was subsequently scraped out by hand and removed. About a quart and change of nasty, acidic foul smelling out with the consistency of honey came out of the drain pan. So we replaced the old oil with 4 qts Supertech and 1 qt MMO and had him drive it for a week. He then added a five minute motor flush and changed the oil. This is the filter that was in for 1 week: And the drained oil + motor flush: After the second oil change and motor flush he said it seemed to be running much better...but a noise was still there on startup and idle. It is hard to diagnoses noises over the phone so I had him post a video of the noise on start up and idle to youtube: Part 1: https://youtu.be/SsVe_aaynLs Part 2: https://youtu.be/dadgAb_2oM0 I know that these Ecotec engines have plastic timing chain guides or other pieces and that GM recommends they be serviced at 70k miles. This poor sludged engine has right at 70k. So judging by the neglected history of the vehicle, the sludged engine and garbage motors engineering I am thinking this noise could be any one of several things: - Timing chain guides broken resulting in chain hitting the inside of the cover - Timing chain not getting enough lubrication because of oil pump sitting in sludge - Noisy lifters or rockers - Exhaust leak What do you guys think?