I've got a 2012 Sonata hybrid (93k miles) that's been making some intermittent engine noise. I can't hear it inside the car when I'm driving, but will hear it sometimes reverberating off of cars next to me if I have the windows cracked open, and last night for the first time I heard it after I had turned the car off and I opened my door to get out of the car, I guess as the engine was cycling down. The noise is not a uniform knock-knock-knock-knock, more of a low-throated rat-a-tata-tata-tat, and again, it's not happening all the time, and never that I've noticed when I first start it up. I noticed it the first time maybe a week or two ago, and the check engine light has come on in the last couple days, so now I'm officially worried, but I'm not getting much clarity from google or YouTube. The oil could stand to be changed, but fluid levels all seem to be fine. Any ideas about what's going on and how it could be fixed? Am trying to avoid major down time and/or mechanic fees, but definitely would rather do that than find myself unexpectedly on the side of the freeway with a busted engine. Thanks for your help!