iPhone 4S Music Dimming Issue

[chillmeow]

Hi,

I wonder if anyone is experiencing this problem. When I play music through my iPhone 4S, the music will dimmed for half a second while playing. This happens very random and not often, but it is very noticeable when the sound dimmed. There is no notification, new mail, new message, or anything, so I am not sure what is causing it. Maybe this is a OS issue or HW issue.

Please comment if you are experiencing this as well.

Thank you!