What does this sound mean??

[Sydsalis]

My cockatiel is 6 months old and has been making these sounds occasionally. Is it trying to sing or does this sound mean something else?

 

[SailBoat]

At 6 months most young Parrots are fairly vocal, it would be unusual for them not to be activity working on expanding their vocabulary.

Since different sounds can have different meanings, it would be helpful to include a video.

 

[wrench13]

The sound of silence?