2006 Corolla - 2 flat tires in 2 weeks

2 weeks ago, one of my back tires suddenly went flat or popped and got torn up on the highway. I started to notice a louder than usual constant noise a few days before the first flat tire. After I replaced the tire, the noise continued when going 60mph+ and the car shook a lot at high speeds. Then today, the other back side tire went flat/popped as well. I got home with a spare.

Both were bought used, with probably 60-70% treads on still. Is it just crappy tires? Or is something wrong? Someone mentioned possibly bad wheel bearings?
This is my 3rd set of tires, 3 are the same brand, the one that just popped was different (a firestone), the one that popped 2 weeks ago was the same brand as the other 3. I forgot what the brand was.

It's a 2006 Toyota Corolla LE. All air in tire was at 31 PSI, as the sticker inside the door says. Mileage is 86,000...

It's front wheel drive. And the car doesn't make any *unusual* constant noises and does not shake at lower speeds, usually shakes a bit around 57+ and a lot around 65+. If that helps.