I'm using a C645D and a C465 both with the latest firmware.  Every time you disconnect from WiFi or have an issue with an SD card, the speaker starts blasting loud warnings and there is no way to disable or adjust this.  It happened during initial setup and a few times afterwards, and it's a big problem.  This "feature" doesn't make sense especially with outdoor cameras.  For example, if the warning goes off in the middle of the night, the noise could be very disturbing for everyone including neighbors.  Another problem is that you can't easily address the issue especially if the camera is mounted outside and requires a ladder to swap a card, or for a general network connection issue.     

Possible solutions through firmware updates could be:

1. Disable the audio warnings on the camera and instead make them appear in the app (This makes the most sense) 

2. Create a setting in the app to control the camera's speaker volume directly or to mute.  (Currently there is a speaker icon that adjusts the microphone and not the actual speaker level.  This should be changed and both adjustments should be easily available on the camera home screen.)