This addon will mute the annoying sounds of WoW. This addon is not a standard addon, please see installation instructions below.
Legion7.0.3-b mutes 12,328 sounds.

Patch 8.1

Patch 8.1 changed the folder structure in preparation for the different Classic and Retail clients.
For this to work post 8.1, simply move the "Sound" folder located in the World of Warcraft folder into the "_retail_" folder.

Please read before updating.
When updating please delete the old version before installing the new one. That means you must completely delete the entire sound folder located in your world of warcraft folder first, then extract the new version.

Is this addon allowed? Can I get banned for using this?!.
As this AddOn does not modify any of Blizzards files, it's perfectly safe to use. If you're after blue confirmation, please read this thread on the battle.net forums.
TL;DR. Yes it's fine and no, you wont be banned.

Requests:.
Initially I used to take requests but due to the increased number of requests, the difficulty of finding certain sound names and the fact I have far less free time these days I can't keep that up anymore. Sorry ! :(
You're welcome to post in the comments, other users may be able to help you find them.

Basic List: Please note this isn't a complete list, it's a small sample to give an idea of whats been muted.

• Players: All race combat grunts as well as emote sounds like train and worgen sniffs. All footsteps.
• Classes: Select sounds like Path of Frost, Fan of Knives, mage armors & portals, hunter pet calls, shaman shields and spell cast fizzles.
• Mechanical Mounts: Choppers, Flying Machines, Goblin Trikes, Mechastriders and Rockets.
• Biological Mounts: Summon roars, mount special, idle and footstep sounds for most mounts. Dismount sound also included.
• Battle Pets: Idle sounds like Lil'XT, Lil'Ragnaros, Singing Sunflower and Thor.
• Hunter/Mage/Warlock Pets: Creature combat sounds, footsteps, flying and idle sounds. Mage elemental loops also included.
• Voice Acting: World bosses, Rhonin & Kalecgos city speech and Headless Horseman speech.
• Toys: Piccolo of the Flaming Fire, Train Sets and Brewfest Mole Machine.
• Daily Hubs: Isle of Thunder, Isle of Quel'Danas and Tol'Barad.
• Misc: City clock sounds, ethereal vendor hubs, waterfalls, rivers, beaches, fires and fireworks.
• Battlegrounds: Victory/Defeat, Alert and Herald sounds.
• Instances: Select boss speech and combat sounds, loops sounds like the beating heart from SoO. All instance portals.
• Creatures: Kovok, Elemental loops and deaths.
• Tradeskills: Alchemy, Leatherworking, Engineering, Blacksmithing, Tailoring and Jewelcrafting sounds.

Installation:

Extract the "Sound" folder to your World of Warcraft > _retail_ folder.
To uninstall simply delete the Sound folder.
To unmute specific sounds delete the corresponding sound file. I know a lot of the sound files arent named anything helpful in finding out what they're actually used for, this is unfortunately Blizzards doing and out of my control. Sorry!