Let's see. You took the vehicle in to the dealer with a legitimate problem
and were told to not worry about it. Here's your options:
1. Call the dealer and speak to the service manager. Make it clear that
you intend to spend zero money there if they cannot demonstrate within the
warranty period that they're capable of fixing your vehicle. My take:
"Failure to fix my vehicle within the warranty period is one thing, but
don't expect me to pay for this privilege." This will be especially
effective if you've been a good customer at this dealer.
2. Find another dealer who cares more about meeting their obligations
than being too busy with other work to car about actually putting effort
into finding and repairing your noise.
3. Call Hyundai Customer Assistance (800-633-5151) and ask them why the
dealer is refusing to repair your vehicle.