the soudns are all done clientside. It only plays the alternative sound if there is one, so if you delete the 2nd sound, you wont hear nothing half the time but it will just keep playing the first one.
The sounds are called WAM1xxx1 and WAM1xxx2. Which one is which, I dont know. They are in the master.dat in data/sounds/sfx and if you only want one of the sounds, you can delete one and rename the other if necessary to 1xxx1 and repack the master.dat, though I have no idea if that works correctly as far as the repack goes. A safe way to do it is just to copy both sounds and overwrite the one you dont like and then insert both of them into aopclient/data/sounds/sfx as they will overwrite what's in the master.dat.
I personally prefer the fallout 1 sound and since this really is all clientside and I just laid out the instructions, feel ree to have a go at it.
Basically, the fallout 2 way of changing sounds still applies as far as the naming convention of the sounds goes, so using this article for the names (the sndlist bitsize and that other shit does not apply
http://falloutmods.wikia.com/wiki/Making_weapon_soundsheres a simple ascii/decimal converter
https://www.branah.com/ascii-converterAnd now you only need the balancing fopros that are posted somewhere in the lobby to get the soundid for each sound you would want to change.
Fonline engines does read .wav just fine but since the vnailla sounds are acm, you would need the same filetype to workd as a client replacer.