Ringing noise/sound on recorded videos?

[Eminemdrdre00]

I just recorded a video on my iPhone3GS and noticed a ringing sound during playback. I've read here that it happens if the phone is on vibrate, but mine wasnt. Is this happening on all phones?

Edit: Yup just uploaded it to the PC and all I hear is the ringing noise. I didnt even talk during the video, just wanted to test out the new TwitVid app. You can hear it for yourself here:
http://twitvid.com/1A588

 

[Eminemdrdre00]

Anyone else hear this on their recorded videos?

Edit: I just figured out what it was. It's that high frequency noise that the 3GS makes whenever the phone makes a sound. When I press record on the video camera, it makes that beep which triggers that high frequency ringing noise. Since the mic is right next to the speaker, it picks the sound up easily. I suppose recording video when the phone is on silent mode would fix it, but I paid $400 for this, it shouldn't be making that sound in the first place.

Did I get a bad phone, or does every 3GS have this issue (those that can hear it).