If the car is starting to shake, then there is a problem.  The best advice I can give you, since I have a Hyundai, and I love it, is to take the car in for a check up at the service department of the Hyundai dealership.  I almost made a big mistake when I decided to take my car to a near by oil change place, instead of to the dealership. They were going to change the powering steering fluid for me and told me that they had the kind that my manual recommended.  My dad said to make sure it was the correct kind because if not, I could have big problems with the motor.  I insisted on looking at their brand and compared it to the ingredients in the manual.  Guess what, that stuff would have given me big engine problems.  The Hyundai dealer said that if I had put in the wrong brand, they would not have honored my warranty.  Your warranty is up, probably, but if there is a problem, you need HYUNDAI PARTS and fluids, for sure.