Have you tried correctly bedding them in yet? Mine would howl until they warmed up once I got it, and I had to wait for dry conditions to bed-in mine. Typically, I find a clear, dry stretch of road I can get up to 60 MPH on. Then, I repeatedly drop from 60 down to around 15-20 MPH, careful not to come to a complete stop. After 3 or 4 passes, I will then drop to around 45 MPH and will only get down to around 5 MPH and let the brakes cool during this phase. After about 3-5 minutes of no complete stops, they're cool enough to allow for complete stops without pad material transfer issues (and hence "warped" rotors). Also, the Veloster doesn't use a nested drum brake assembly in the rear rotors to act has a parking brake, and instead has a mechanical drive to the piston in the rear brake caliper. When bedding rotors I'll sometimes use the parking brake to fully stop the car if it's necessary, but that may not be advisable here as you'll see some pad transfer once the rotors are hot enough to "burn" pad imprints onto both sides of the rotor. If this does happen, you can get back up to speed and repeat the main cycle to burn those transfer deposits back off since the rotors are still hot.
But ultimately, this relies on finding a nice, controlled, clear stretch of road to complete this. As you're using a peak speed that's below many many highway speed limits, it's possible to use them. Just keep in mind that this behavior will confuse nearly everyone else around, and law enforcement officers may want to ask you a few questions while you're trying to cool your brakes evenly before fully stopping. ;-)