I don't have an Elantra, but I did have a very problematic Saab convertible for a couple years. It was bought second-hand and had a clean Carfax, but the suspension felt terribly wrong. It was almost dangerous feeling the way it would "float" down the road. It almost felt like the body was sitting on a waterbed.

Some dismissed it as just being the consequences of being a convertible, but I've driven plenty of similar cars that felt nothing like this. I probably put $2500 into the car over 2 years to correct the issue. With every fix, it got slightly better, but it never felt right.

The final solution was to trade it into a dealer. They actually gave me only $1000 less than what I bought it for. So, I didn't get hit too bad. Now it's someone else's problem... hopefully the dealer's.