I have a 2012 Elantra with 97K and never heard this noise until a couple of days ago. I then heard it, a very distinct chatter like sound when starting the engine after it sat overnight and then when starting that night when leaving work and then the next morning. Has started twice since without the sound. I'm not sure if temperature is a factor here. Some MD Elantra owners have this start up noise since new. Since mine is only after 97K I'm thinking something has changed to cause my noise. Would a pcv possibly have anything to do with oil pressure on start up? I use OEM filter and TGMO. How could I assure I'm getting oil to the top end before starting the engine? I will monitor this as the temperature drops this weekend and see if it may be a contributing factor.