The boat you saw was the USCG, and they were checking boats on Monday. I saw them pull over another Captain I know, that runs a Ranger, and they used their siren (one or two short blasts) to get him off plane. I saw them at the ramp when we went in, and I asked them what was going on..."Did someone have a heart attack out there?" He said, "No, we were just checking boats out there". They were also checking at the dock, if you didn't already have your safety sticker, you would be checked. I had mine, so they didn't bother.

As for the underwater alien noise, I can't help you with that one....that sounds really weird.