Ive had my Sprint Iphone 4s 32 gig for almost a year now. It has been working flawlessly up until yesterday. I noticed that when I am on a call and the other peson is talking, you hear a rattle sound in the earpiece. Almost as if something is loose in the phone. It only happens when the other party is speaking. Doesnt happen when on speaker or on bluetooth. Not sure why this just happened. I take very good care of my phone. No scratches, never been dropped. Any ideas?