There is currently a bug in Half-Life: Source when you use the HD texture/models pack. Sound does not work correctly with some weapons or in certain scenarios (e.g. reloading) [1]. See this Github issue for more information. The "hard work" of this script was done by malortie in this issue.
This script automatically fixes your Half-Life: Source so that HD texture/models work correctly. It only works for OSX and Linux, but it should be easy to port to Windows if needed.
[1] There are no sounds when the pistol/glock, magnum, m4 and mp5 reload. Furthermore, the rifle and shotgun have missing sounds.
In order to get your Half-Life: Source all dandy you can do the following steps:
git clone https://github.com/Jorl17/half-life-source-hd-sound-fix/
cd half-life-source-hd-sound-fix
chmod +x ./half-life-source-hd-sound-fix.sh
./half-life-source-hd-sound-fix.shNow go out and be a Freeman!