I have recently switched to a Sena 50S from a Cardo Packtalk, because my friends are all on Sena and have the following issue now:

The VOX is way too sensitive and activates when i accelerate, ride faster than ~65km/h or breathe too hard. I have the sensitivity already set to 1 and updated the Firmware to the newest version (2.7.2). 

Additionally i can't adjust the how much the volume of the music should be lowered when using "Bluetooth-Intercom Audio Multitasking™", which makes the super sensitive VOX issue extra annoying.

I'm using a motocross helmet, so i can't reduce the incoming wind. The Cardo didn't have either issues.