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Here is the answer to use a sound mod in RED TIDE;
Backup your "Red Tide" sound.pak file for safety.
With original "Red Tide" sound.pak or a spare original sound.pak change the word pak to zip.
Extract with Winrar program as ZIP file.
Put your MoW "Ultimate Sound Pack addon" - sound folder into / replace the sound folder of the unpacked "Red Tide" sound folder. > "Yes to all"
Repack this new modded sound folder using Winrar as ZIP.
Rename sound.zip extension to
sound.pak.
Put this back into the "Red Tide" folder.
This answer is from the "[MoW] Ultimate Sound Pack" addon webpage, page 4;
"[MoW] Ultimate Sound Pack"