There was a sub menu that offered audible alerts within the navigation options menu. I just checked it and it worked. I used the exact same file that you down loaded from me earlier.
The alert was simply a loud beep, it actually became quite annoying as it seemed to beep occasionally for other items that were not obvious to me in the short time I spent with the car in spite of un-checking all other POI's.
Initially I thought the camera function was screwed up and then I realised that the database was still showing cameras that were temporarily installed last year during motorway maintenance. I then tested it in known camera areas and it gave an audible beep 4-5 seconds before passing the camera as well as displaying the small graphic on the screen.
My experience was that unless the warning beep was enabled, the chances of spotting the camera on the display would be quite slim due to the small size of the graphics. Is it possible to make the graphics larger?
In respect to waiting for your next update, I fear you may have the same problem as me, that is that when maps are updated, that is all that is updated
The navigation menu structure did not change at all when I had my 2011 E350 updated from V4.0 to V7.0

hence I am unable to even load the cameras let alone receive audible warnings.
To fix this issue I guess we need to understand how to access the navigation control firmware to at least be able to know what revision is installed and of course ultimately find a way to update it.