After engine cools down, timing chain rattle can be heard upon starting the car. Chain rattle means that plastic guides or adjusters are worn, and might go any second. Spoke with Audi rep online, which advises me that this is normal, and expected. Knowing basics of engines and transmission, I didn't believe that something is "life time" and is not serviceable, especially if it's plastic (which tends to shrink and expand depending on temperatures, and then has fractures which snaps). Two different independent licensed Audi shops confirmed that the guides and adjusters has to be replaced in order to prevent catastrophic engine failure. Chain skipping a tooth might mean bent valves, scored cylinder walls and the list goes on. What is lifetime, should be covered by Audi. If it's promised to be lifetime and needs no service, shouldn't break. If it breaks that only means design flaws, which are obvious in this engine. Yes, car isn't new, but the parts were lifetime, so I'm expecting them to last until engine is worn out, not the parts that are lifetime. If NHTSA will do full scale investigation. Will be obvious that large amount of S4's ranging from 2004 to 2007 are affected. Even 10% is large number, considered the costs of fixing what is "lifetime" according to Audi, and when it fails they leave their designs flaws for you to figure out. Hopefully justice can be brought to light as to what Audi tries to turn it's back to. Symptoms: Chain rattle upon start. Chain rattle doesn't go away while driving. Check engine light, loss of power or catastrophic engine failure.

- Rahway, NJ, USA

On Saturday morning 12/15/2014 start my card and heard a rattle noise on the engine, first time it make that noise since I bought it. On my way to work I started hearing the rattle noise again but this time it was louder I was driving around 40 mph when this happened. The car started vibrating and kept making the rattle noise on the engine. I just bought this car not even a week ago, and already started having engine problems. I took it to the mechanic and found out the engine might need to be replace soon, since that's a common problem with this cars and that that's one of the signs that the engine might go bad soon.

- Hammond , IN, USA

Audi claims that the timing chain on those vehicles are lifetime and does not need to be service. Unfortunate the timing change tensioners are made of plastic which the wear out at about 50K miles, causing a start up rattle and eventually engine explosion from the chain coming of the guides and destroying the entire engine and causing a massive accident at high speed. Hundreds of problems like this one are reported online from thousands of people even youtube videos. Not to mention that every time you bring your vehicle and complaint to Audi the claim that the rattle is normal; just to find out that is the first clue of future engine failure.

- Hamden, CT, USA