For the past month my Samsung Galaxy S3 has been making yawning noises. No im not crazy, I have witnesses. Why is it doing that and how can I stop it?
There could be two reasons for this, I am assuming I know what sound you are talking about since you have not provided an audio example.
You have sounds for phone sleep and phone awake in your settings and/or you have notification sounds enabled.
You have skype installed with the notifications on for people login/logout, the logout makes a yawning sound.
Check this out and I guess one of them is your root cause :)