So much for warranties....I have a 2013 Elantra and I have the same problem. It started squeaking about a year ago. I called the Dealership, they suggested squirting WD40 in the hinge. We did, twice, and then the third time we used silicone. This past April, I took it into the shop, they used some kind of white grease, I know this cause I they left residue on the outside casing of the door. This past July it came back even louder, so my sister oiled it for me. I called the shop again complaining that about every 2-3 months it comes back. It does not do it if it is raining or I wash the car.
The Tech explained to me that it is the bar that slides in and out of the door, and the rain acts as a lubricant. I told him that I bought a 2001 Elantra and NEVER had this problem, and loved it so much that I bought another one. It is apparent to me that the material they are making this piece out of is different and needs to be replaced. I said to him, "my concern is that I have a 5 year bumper to bumper warranty and every 2-3 months I have to bring it in. If my warranty expires, will I not only have to keep bringing it in, but have to pay to have you grease the doors?"
I have since called Customer Service who advised me the next time I take it in to let him know and he will call the shop and speak to the technician to see if it can be resolved. I have an appointment this coming Tuesday, 8/18/15.