Something Schlunking Around In The Tank?

[tinkering]

2010 Mazda 3 GS
When stopping, this noise sounds like there is a stowaway in the trunk who's getting bed sores, and throws his body over. It sounds like the fuel pump has come apart and is thrown back and forth by the fuel in the tank. Could it be a baffle that has come loose in there? It's way more than a rattle, or a clunk. You can hear a back and forth sound when initially stopped, like the momentum has gotten the fuel to slosh back and forth which throws something around in there.
Anybody recognize something similar to this?

It doesn't sound like a loose sway bar link. It's when you brake to nearly a stop, then let it off and on again quickly... like you get the fuel sloshing back and forth and whatever is loose is moving with the fuel in there.