Thumbs down [Q] S4 GT-I9505 LTE sound echoes: software vs hardware ?

Hi
Now I have S4 GT-I9505 LTE - 4.3 omega v.19 custom rom

when I make or receive a call, the sound has too much echoes for both sides.
I've had some advices to fix this problem (reloading my Stock rom 4.3 for several times) but the result was "no benefit"
Then I transferred to "4.3 omega v.19 custom rom" but the result was the same.

Does anybody know:
1- Wheather this is due to a hardware malfunction or something about the software?
2- Has anybody really managed to fix this problem with any software changes? And;
3- If so, how?

Thanks, have a good time...