Viber listening during dialing, who faced?

Question

Viber

Repeatedly encountered the following glitch Viber:
When dialing to the interlocutor, before he "picked up", I hear the vibration of the remote smartphone and the sounds surrounding it, while he does not hear me and he watches the incoming one, which he either cannot answer or does not hear and therefore not suitable for a smartphone.

Who faced similar glitches of Viber?
Maybe it's a hidden function for listening? which randomly works?