BLOWER MOTOR for 2012 Hyundai Accent|97111-1R000
Not sure how well you can do this, but it's a $112 part MSRP, and it's no more than an hours labor to change it, and it's VERY likely the problem.
I would try to see if the dealer will swap it out for you and hang onto your old one - if the new one fixes it, he submits a warranty claim. If it doesn't, he puts the old one back and keeps trouble-shooting.
(Actually, on modern cars, he probably could replace the blower under warranty and if that doesn't clear the problem, replace something else under warranty, etc.)
(Other option would be to buy and replace the blower yourself and try to get the dealer to re-imburse you under warranty if it fixes the problem - but that is even harder to work out with them - even though that probably makes extra money for him ...)
Or just spend $90 at the link above and be done with it (if that was the problem), and not worry about the warranty - but that would be your last resort.