It was definately a helo flying too low (about 75ft or under). I've looked at the stock doctrine and its likely the active pinger was on if the helo was prosecuting a contact.
The sensor is still there, but in stock DW it's purely vestigial because all the dipping instructions are disabled so the MH60 when controlled by the FFG doesn't go flying off on its own.
Why they didn't just make a second doctrine, I'll never know. Then again, the stock dipping commands don't work either, so I guess they figured some modder would take care of it eventually. Go figure.
Cheers,
David