Heres a good tutorial for you to use:

First you need the addon file/.gma file of this addon. You will also need to find a program called "gmad.exe" in the bin folder of the "GarrysMod" folder directory. (To access this folder you can go into Steam and click Properties and go to local files and then click browse local files)

Gmad.exe's file location is in "GarrysMod\bin" You might have to scroll down a bit.

Addon's file/.gma file is in "GarrysMod\garrysmod\addons" I think. Once you are in the addons folder, Just search things in the file explorer like CBH or SW1500.

Once you have found the .gma file of the addon and gmad.exe, Drag and drop the .gma file onto gmad.exe and then check the addons folder. There will be a folder with the same name as the addon's filename. Go into that folder and eventually you might find the sounds folder and the audio files for the engine, horn, etc. If it doesnt work then.. well.. I can't really help you.

Sorry if that was too much to follow or too long.