New mystery: Buzzing

There is a new mystery in the box!

Mood: old horror movies, a mad scientist, mutated insects
Time: 3-4 hours

A herd of cows was found dead on a farm near a small town. They had gone out to pasture less than an hour earlier, but their carcasses were horribly swollen, and there were no tracks on the ground nearby. A menacing buzzing sound is coming from beneath the ground.