Omnipresent sun or overwhelming heat, this is a sound effect that is widely used in films. I made this sound in the studio, failing to find it in nature. Maybe it's an insect? If you know more about the source of this noise, tell me. Duration: 00:44.
Song of robin, a garden bird. He cries from a tree, spacing his songs for 2 to 3 seconds, then stops, changes his tree and starts again a few dozen times and so on around his territory. Duration: 00:02.
Several beeps of an active sonar. This is a low frequency sonar (long range but low definition). It is a triangular wave of 1030 Hz frequency easy to put in loop. In reality, a military submarine usually has passive sonar, more sonar info: en.wikipedia.org/wiki/Sonar. Duration: 00:31.