Car was making an intermittent rattling/knocking noise. Took to dealer and mechanic test drove it. He got out onto road and hammered the throttle and it sounded like engine was about to fly apart. I suspect he had already guessed what was wrong before we took test drive. He diagnosed as failed con rod bearing which I found by finding this site is an endemic problem with 2011-2014 Sonatas. Hyundai Canada is fixing it but unlike US owners having their power train warranties doubled I will only be getting a 12 month/24,000 km warranty on new engine. What is really ticking me off is that Hyundai knows this engine fails suddenly and without warning and I was never notified of that. My wife uses the vehicle to come home from work late at night and we live in a very rural area without much traffic at that time of night.

screeching

At about 43000 miles a loud screeching noise began emanating from near the turbo when I would start the car up after the car sat for about an hour. The screeching would then become louder after the first accelerations and then dissipate. Dropped car off at Hyundai who informed me that I needed a new engine due to a low end noise also coming from the engine.

Update from May 3, 2016: Dealer says that the engine replacement issue is not a part of the 2011 - 2012 engine recall issue, but could not tell me what the issue was. Sounds very suspicious to me.

The noise in the car is so loud. When sitting in the back seats, it's unbearable. Took the car to the service department twice (in 2014 and 2015), they said it's the tires which make loud noise. The tires are in good shape. I think there is a defect. We bought 2011 Hyundai Sonata, there was no problem even when the tires really worn out. We love the 2011 Sonata. If the problem is not solved, no more Hyundai Sonata for us. The engine noise in 2013 Sonata is much louder than my 2005 Toyota Sienna!