I decided to change sounds from GregTech 5. They are in gregtech-5.09.19.jar\assets\ic2\sounds\
I also download Sn0wZone to see how it works.
I placed my sounds with the path mypack.zip\assets\ic2\sounds\
I use *.ogg files with the same duration as in gregtech-5.09.19.jar\assets\ic2\sounds\. But it doesn't work. But Sn0wZone sounds work fine!
What I did wrong?