I have a K610i@W660 and I applied a patch that removed that annoying sound.

But, I see you're using a C905 and I'm pretty sure it ain't possible. I think you should be able to enter your phones filesystem and remove the voicerecorder-files manually.

In my phone, there's a file called "voicerecorderbeep.mp3" or something similar to that. Remove that one from your phone and everything should be running fine. They should be foudn in: tpa/preset/system/sound


Good luck!