No no, I specifically observed it. And made others observe it too. And sometimes it ring sometimes it doesn't. I tried changing tones, resetting the phone, restarting it and what not. My phone is in warranty so I'm thinking to claim it. Some people said if you give your phone to be repaired chances are that It might catch some other problems. What should I do?

Hmm.. Sometimes, I'm like this and think that my phone doesn't make a sound. But when you come to think of it, you may just not really notice your phone because you're too busy. Try using a louder and longer ringtone and see if this time you hear it and notice it. :)