Default Miui 4.2.28-Answer delay

I have smartphone zte z5s mini nubia with custom ROM miui 4.2.28.
Every time I slide the bar for answering an incoming call and I say "YES...", the caller can not hear my "Yes" and I can not hear him/her for the same short time, as well.We can hear each other after 3 seconds.
What should I do?
Thanks