Its still electromagnetic waves not pressure waves so they're not audible.

Still, I'd recommend not being very close to the transmitter if its putting out megawatts of power.

You know that hum you get when mains powered audio get gets a certain kind of interference? That's 60Hz (or 50Hz depending on where you are) of moving air. It's not the 50Hz electromagnetism you h4ear though, it's that getting picked up by the amplifier and played out through the speakers which move the air.

87Hz is right about the second lowest F key on a piano. (the 21 key up from the lowest note on an 88key piano), or the low E string on a guitar at the first F fret.

Nah, it’s electromagnetic & your ears are too small to intercept the transmission to any kind of significant extent.

A few MW sounds a lot, but the inverse square law applies - once you get to the ocean the power density is going to be very low. Plus penetration into the ocean itself isn’t going to be great - there’s an impedence mismatch between the water and the air.