Here are some pictures showing how to disassemble the Ben NanoNote
Under the thin metal piece over speaker and microphone is glued to the plastic underneath it. There are no screws or anything under the metal piece. If you still attempt to lift it off, chances are good that you will bend the metal and will not get it flat anymore. So unless you have a good reason, I suggest to keep the metal piece where it is, you can easily lift off the entire plastic it sits on, together with the metal.