The shrill, unnatural sound carried across the battlefield, chilling the hearts of all who stood in their path.

I could not account for the strange tone of his voice, an unnatural sound, how it was almost, but not quite, kind.

And in the echo, he heard another, unnatural sound.

The whole house seemed to shake, and the wind whistled down the chimneys with a strange, unnatural sound.

The night was very still, and we waited, listening, our ears seeking out the unnatural, unexpected sounds, but there were none.

There was no unnatural sound, no real warning, yet she knew.

An unnatural sound, high heels clacking on paved ground, got a better response.

The eerie, unnatural sound ripped shockingly through the charged atmosphere.

This tended to give the voice a distinctly mechanical, unnatural sound.

That produces an unnatural sound but helps the listener understand.