Marisabel Discovers the Whispering Chest
Marisabel discovered the wreck of the Silver Blade near the island where she grew up. While exploring the wreck, she found the Whispering Chest with a notice in Merfolk language that reads "Do Not Open". Unsure of what to do with it and as she previously found earrings that allowed her to talk with Merfolk, she went to a meeting place on an island near Golden Sands Outpost to return this mysterious chest to the mer people.
However, the Merfolk reacted viscerally to the presence of the Chest, warning not to open it or throw it in the sea. The mer fled as soon as the Chest began to hum.
Source
Tales From The Sea of Thieves