install sound:

1. download gta ivaud 1.1.5(http://www.gta4-mods.com/tools/gta-ivaud-v115-f3996)

2. open sparkIV(recommend), browse to GTAIV main folder/pc/audio/sfx/resident.rpf (select resident in the left-side first)

3. export WEAPONS.ivaud to the desktop

4. open gta ivaud 1.1.5, and open the WEAPONS.ivaud

5. look for and replace SNIPERRIFLE_SHOT1_L.WAV...SNIPERRIFLE_SHOT1_R.WAV...SNIPERRIFLE_SHOT2_L.WAV...SNIPERRIFLE_SHOT2_R.WAV...SNIPERRIFLE_TAIL_L.WAV and SNIPERRIFLE_TAIL_R.WAV, scroll down to: number #135-138, 141, 142

6. SAVE it, and import WEAPONS.ivaud again with sparkIV(openIV can't do this)