What's causing "upsweep," an unidentified sound NOAA has been capturing under the ocean since 1991?

very strange
could be a flying saucer
giving off signals? LOL

Oh like you don't know with your one Illuminati eye.

That sound is too fast coming from under the water.  They must have sped it up a bit.
Sounds like a whale to me. 

That's an intriguing question about a mystifying phenomenon. I'm certainly not going to guess at it since nobody with the qualifications to do so has had a decent guess, either. 

It's interesting that it wasn't noted till 1991 and started to wane after 1994 but still persists. It's also interesting that it can be detected almost anywhere in the Pacific.

Here's an article that provides some of the background but no real answers.

have no idea, never heard of it