Rampage thermite ramp up sound not in sync with timer

The ramp up sound doesnt sync with the last part of the timer, so you think its finished, but there is an annoying last 0,5 sec left of the ramp up so you ADS then it cancels.... 

So the audio and animation doesnt sync well up with the timer. And also why does it cancel when I ads when I've placed the thermite and closed the handle and lid.

It should be more clear when the ramp up is done and not be dependant on watching the timer instead of just knowing from the animation and audio. There should be a clear end sound so you know its done. Like the clear/loud/distinct sound of closing a lid or a electronic sound / indicator from the weapon as a indicator of "Done".