Problem with Midland GXT710

Hi all,
I purchased a set of Midland GXT710’s about 2 months ago. I have powered them on no more than 10 times, and actually used them only twice for range testing and weather alerts. One radio is working perfectly, while the other is on the fritz. When powered on, the display briefly blinks, then goes blank followed by an obnoxious, constant squealing. It also vibrates continuously. I can turn the volume up and down, but none of the buttons are responding. I’ve contacted Midland and I’m not sure if they’ll honor the warranty since I purchased the radios online and no longer have a receipt. Any ideas on what could be going on? If its something simple that requires popping it open and messing with it, no problem. But anything past rewiring/circuitry is beyond me. Any suggestions would be great. Thanks!