@xover88 I created a new sectoid scream for starters. Tried to replace just that one in your SAMPLE2.CAT, unpacked it with CatPacker.exe, overwrote 0010_2.wav for the scream just to try the process.
I wanted to replace 0A 1E C4 01 3E 2B sectoid scream with my wav.
Packed the wav files, but CatPacker either messed up the indexes at unpacking or repacking, because now all sounds are playing totally mixed up.
What file naming of wavs did you use and what software to assemble the sound effect set?