First of all, find the game on your Steam Library.
Once you find the game in your library, click on the little gear in the corner and go to "Properties".

After that, click the "DLC" button and uncheck the Ryder White DLC.

That should fix it! But the downside is that you can't play the DLC, that's why we are going to "The Easy Way"!

Make sure you have the DLC installed!
First of all, you need to download this[drive.google.com] file. We are going to use it soon!

After downloading it, copy the file inside the .rar file and place it in the following directory:
C:\Users\YOURNAMEHERE\Documents\DeadIsland\out\Data

If the Data folder does not exist in the out folder. Simply create one!
After that, paste the file you downloaded into the Data folder and it should be working just fine!

FOLLOWING THE STEPS IN THIS SECTION IS COMPLETELY UNNECESSARY AND SHOULD ONLY BE FOLLOWED IF YOU FEEL THE NEED TO DO SO.

For this one, we are going to need two things: 7-Zip[www.7-zip.org] and Notepad++[notepad-plus-plus.org]

First thing to do is to make sure you have the DLC installed. After that go to the game's directory which is located in:
C:\Program Files (x86)\Steam\steamapps\common\Dead Island\DI

Locate the DataDLC0_En.pak file in the directory and open it with 7-Zip.
After that, open the Data folder inside the .pak file and drag and drop the "texts_DLC0.scr" file to your desktop or any place of your choice.

Right Click texts_DLC0 and click on "Properties". Turn "read-only" off and apply changes. After that open the file with Notepad++.

With Notepad++ open, press CTRL+F and search for String( "MenuMusic_Common", "" ) and press enter.

After doing that, delete this completely. Then, click on "File" on the top left corner of the screen and save your changes.

With your now modified texts_DLC0 file, copy it and go to this directory:
C:\Users\YOURNAMEHERE\Documents\DeadIsland\out\Data

If the Data folder does not exist in the out folder for you. Simply create one yourself!
After that, paste the file into the Data folder and it should be working just fine!

The reason the menu music is muted is because the string ("MenuMusic_Common", "") located in the texts_DLC0.scr file controls the menu music and some developer accidentally left it blank. So nothing plays!

This section is dedicated to credit @DeadIslandHelpCenter on YT for helping me out with this. This guide would not exist without the help of them!