Sniper rifle sound problem

I'm in the process of creating weapon sound packs that work without bugs (such as rain/reloading). I've noticed that a slight pitch shift/distorted effect is applied to any sound the sniper rifle uses whenever it's fired in singleplayer. Even the original sniper rifle sound seems to have this effect too.

However, for some reason, the sniper rifle sound works fine in SA-MP, playing the same sound as the .wav files. The "country rifle," which shares the same sound files as the sniper rifle, will also work fine in both SA-MP and singleplayer. It's only the sniper rifle which sounds different.

Video: http://www.youtube.com/watch?v=pO_Idko38xU&feature=plcp

Anyone know how this can be fixed?