You have to adjust the volume while the alarm is active. So drive towards a speed camera you know about and when it goes off, turn the volume up. You need lightening reactions!

 

I had the same problem. The answer is to adjust the speech volume when directions are being given. The camera alert volume is linked to the turn instruction volume. I set a route before I left home and as soon as I started to receive instructions I turned up the volume and immediately cancelled the route planner. Pleased to say it worked. This instruction is now shown on the MY21 owners online manual.