Shaking iPhone 4 sound

[lol_release]

With my iPhone 3G with the mute button on mute I would hear a sound when I was to shake my iPhone. If I was to take off the mute the sound would go away because the button was held in place.

With my iPhone 4 I always hear a noise when I shake my iPhone muted or not muted.

Can anyone else confirm an internal sound when shaking their iPhone 4?

Thanks

[thechronic]

I think its the sleep button