G'day,

This is a version of the 'dweller on the threshold' phenomena, which can be thought of as a test.

To pass the test, face it, command it to go away, or just ignore it.

It is unlikely to happen again if faced.

Alternatively, you could have tuned into some astral noise that just sounded like this...some kind of static.

Regardless, this is nothing to worry about.

Robert