Backlight for thunderbolt display failing at full power

Just bought an Apple Thunderbolt display off Craigslist, 27” (A1407 2011 model). The backlighting on the display bugs out when it’s at full brightness (as far as I can tell, the display works as intended at half brightness). I got a deal on it - so I’m mainly wondering if it’s something simple that I can repair, or if I should try to run down the person I got it from for a refund?

As I increase brightness to much beyond halfway, a few things happen:

1. A slight buzz sound. The volume increasing proportionate to the brightness.
2. Intermittently flickers (less than 1 second going totally black, then back immediately) 3 - After a few minutes, it goes completely black (it’s just the backlighting for the LCD, it’s still connected, and if I shine a flashlight on the screen and move something, I can barely make out a dim existence of a non-backlit display).
3. Unplugging the monitor from thunderbolt does nothing, only unplugging from power and then plugging back in will get the backlight to come back.

Things I’ve tried:

• Cycling power to devices
• Software updates (  Port Micro Firmware Version: 2.0.7, and Firmware Version: 26.2)
• Multiple different machines with and without uSB-c adapter
• Different thunderbolt cable (vs the built-in one)
• No other devices are plugged in besides power and thunderbolt.