Bought this car in the summer and the issue was not as noticeable. When first started, and until the engine warms up, there is a noticeable mechanical clicking, clacking noise coming from the top of the engine on acceleration. It sounds like a marble in a glass gar being shaken. As the temperatures drop the noise gets louder and louder. It sounds like a bad lifter or valve train parts are loose. I was told that it is a GDI pump by the dealer and that it is perfectly normal. The only trouble with that theory is that this car does not GDI. When I told them that they just kind of shrugged it off. I find it hard to believe that Hyundai would make an engine that sounds this bad when it is cold on purpose. I'm afraid that there is not enough oil getting to the top part of the motor and that it will eventually cause some kind of major failure. I guess I'll just have to hope it occurs before the warranty is up.