Yes 2 ways to do it.
1. with lukas viewer ( settings )
2.by pressing the button ( cant remember if its just 1 push of button or press and hold for x seconds )
Either way if sound is deactivated the ( . ) on top of the display should be gone, if sound recording is ON the ( . ) on the upper part of the display will blink ( 3 second interval ) ( page 8 in the manual )
The cam should remember this setting when it is turned off, at least mine did both with shipping firmware and the current Fc29 firmware.
Your cam display current firmware when booting, if it is Fc 29 you have to use the corresponding Fc 29lukas viewer witch can be Down loaded here.
http://www.lukashd.com/gnuboard4/bbs/board.php?bo_table=eng_viewer&wr_id=25
video on viewer install
link to Fc29 firmware if needed.
http://lukashd.com/gnuboard4/bbs/board.php?bo_table=eng_firmware&wr_id=26
when i flashed my cam i did it this way.
1. Download Fc29 lukas viewer and install it
2. use Fc 29 viewer to format a small 1 gb SD Card i had lying around
3.download and unzip Fc 29 firmware ( 3 files when unzipped )
4. copied the 3 firmware files to the root of the 1 Gb Fc29 viwer formatted SD Card
5. put 1 Gb SD Card in the cam, and started it up. ( camra now upgrader firmware )
6. turn off cam when update is done.
7. inserted 64 Gb SD Card witch allso had been formatted on my computer using the Fc29 viewer
If you dont feel like messing with the firmware, it is allso easy to remove the soundtrack when edeting the videos in software ( Windows live movie maker or simmilar )
Hope you can use some of this.
PS. i am on my way out the door to film the approaching storm, if i suvive i will be back in front of the computer in 6-7-8 houres.