That's actually a new one to me and sounds more like air whistling. Did it start all of a sudden? If so, what did you change on the bike recently or happen to the bike that was unusual? Maybe a vacuum or intake leak?
Maybe to localize the noise specifically use the fuel tube stethoscope method. Put a yard of it up to your ear and move the other end around on the area of the bike making the noise and try to localize it more accurately. You should be able to confirm it's the water pump or maybe it's something adjacent that area.