Nutone doorbell buzzing when Ring Pro is pressed

I've used the Ring Video Pro Doorbell with my Nutone doorbell for 2 years with no issues. Recently, when the ring doorbell is pressed, the Nutone will sound the first DING, make a loud buzzing sound for 10-15 seconds, then sound the second DING. The actual Ring chime sounds normal. I recently transferred account ownership to my name, but all of the hardware was untouched (just had to repair everything in the app). Any idea why the Nutone doorbell started making this sound?