In real life, when a person drinks any drink from a straw, you would only hear a noise when his/her drink is about to finish.
I mean this noise:
But in TV shows, whenever you see someone drinking from a straw, it never matters how empty or full the drink is. That sound will always be heard.
Is it done deliberately (sound effect is added later) so that audience can know for sure that the person is really drinking (as opposed to : just putting the straw inside the mouth and not sucking anything)?