Perhaps they've changed the app since your hack - but that seems unlikely since your post is pretty recent - but that file is not on my device.I've used a workaround (needs root access) to 'silence' the annoying sounds.
mv /system/media/audio/notifications/S_Charming_bell.ogg /system/media/audio/notifications/S_Charming_bell.ogg.old
The part that drives me crazy is that the app plays tones for incoming messages even while the app is in the foreground. This is idiotic. I took apart the APK and found the offending file. It is in /res/raw/incoming_fg.mp3 inside the APK. Just as there is presently a checkbox for "Outgoing message sounds" (to let you turn them off) there should be a checkbox for "Incoming foreground message sounds".
I don't want to turn off all notifications - but I don't want the app to make a peep while it's in the foreground. Since the incoming message sounds are already in two separate files (incoming_bg.mp3 and incoming_fg.mp3) this should be trivially simple. Viber should be embarrassed that users have been complaining about this since 2012 with no response. What they fail to recognize is that for every user that gripes about it there are probably 20 that just said "What moron designed this thing? Uninstall.".
The sad part is that it is an otherwise good product that has the unique advantage of running on just about every platform. It almost feels like there is someone on the dev team that just can't bear the thought of people not hearing his dippy incoming_fg.mp3 for the entire damn time they are using the app.
I'm going to try disassembling the APK, removing or replacing incoming_fg.mp3, putting it back together, signing, and zip aligning it. Maybe that can save this app from itself (or rather its developers). You'd think that with the massive monetary value associated with these products (look at the sale price of WhatsApp recently) that Viber wouldn't want to drive off customers over a stupid checkbox. Even if the configurability was exposed inside a settings database so we could do it ourselves without anything added to the front end of the app - that would be better than nothing. Or have the sound files external to the APK so we can delete them. Or do virtually anything other than what they are doing now.
OK, I'm done ranting.