Volume goes down after 5sec playing on ported roms

Hello, I´m having this problem. On some ported roms by me on MT6592 device, the volume goes down while I play any sound for more than 5 seconds. It goes down but no the volume bar. After this you cant ear loud sound until you pause/stop sounds and wait 2 or 3 seconds. Then when you play again it sounds OK by 5 more seconds and again goes down. The diference between normal sound and final sound is like going from 100% to 20%.

I cant find any lib that solves this problem.... Somebody knows something about?
Thanks!