Question [Q] Xperia U Kitkat Maclaw's rom background noise problem


I am using kitkat rom by Maclaw studio ( (h t t p : / / g e t . m a c l a w . p l / ? i d = 379)
Whenever try to make Viber calls there is a lot of background noise and the person on the other end can barely hear me. Normal calls work just fine. How to fix this problem?
Please help