When you tap gently near the top of the iPhone 4 on the back glass, do you hear a rattle? I sure do. I also hear it every time I set it down. I'd like to know if it's normal or if I need a replacement.
I made the appointment with the Genius Bar today. The first thing I did when I walked in was to check the demo units for the noise. They all did it! If you gently tap the four back corners of your phone, you'll notice that when you tap the corner with the camera it sounds like something is loose. So the bad news is the phone doesn't sound solid.
The good new is that Apple replaced my phone because of the speaker issue.
I have tried this several ways and there's no noise of any kind. It must be just your phone.