Just discovered another reason why sounds may not work properly in SP.
In the soundaliases files, each sound has a line of its own, which looks something like this:
Code:
weap_shotgun_fire_pump_plr,,weapons/shotgun/wpnfire_shotgun1.wav,0.91,0.97,wpnplyr,0.95,1.05,500000,,local,,,,0.85,all_mp,,,,weapon2,,,,0.2
OR
Code:
weap_kar98k_sniper_fire_plr,,weapons/kar98k/kar98_sniper.wav,0.78,0.86,wpnplyr,0.95,1.05,500000,,local,,,,0.85,!toujane !elalamein !eldaba,,,,,,,,0.2
In the first example, you can see "all_mp" near the end. This makes it work only in Multiplayer. All you have to do is remove that and it should play in Singleplayer as well (as I learned the hard way).
The second example contains a section near the end that looks like this: "!toujane !elalamein !eldaba" This excludes the sound from certain SP maps. Once again, just remove that section and you'll be fine.