* Howl: This is the most likely answer. Wolves and dogs are known for their long, wavering, high-pitched howls.

* Yowl: This is a similar sound to a howl, but usually shorter and less melodic. Cats are known for yowling.

* Whistle: Some birds, particularly birds of prey, can make high-pitched whistling sounds.

* Siren: If the sound is very loud and mechanical, it could be a siren.

To help me narrow it down, can you tell me:

* Where did you hear the sound? (e.g., in the woods, in your neighborhood, in a movie)

* How long did the sound last?

* Was the sound repeated?

* Did you hear other sounds with it?

With more information, I can give you a more accurate answer!