Solution: (I have only verified this works on XPS 15 L502X).
Go to Device Manager
Open Audio inputs and outputs
Right-click on current sound driver and uninstall
Open Sound, video and game controllers
Right-click on Realtek driver and uninstall
Open Microsoft Edge and go to Dell Drivers & Downloads
Browse for a product and select XPS L502X
Change OS to Windows 7
Open Applications and select QuickSet driver
Download and save to folder (DO NOT RUN)
Open folder, right-click setup file and click properties
Go to Compatibility and select open in Windows 7 compatibility mode, select OK
Open setup file, follow instructions and install
Open Microsoft Edge and go to Dell Drivers & Downloads
Browse for a product and select XPS L502X
Change OS to Windows 7
Open Audio and select Realtek driver
Download and save to folder (DO NOT RUN)
Open folder, right-click setup file and click properties
Go to Compatibility and select open in Windows 7 compatibility mode, select OK
Open setup file, follow instructions and install. Computer will restart.
Now it should work but if it doesn't, go to C:\Program files\Realtek\Vista
Rght-click setup file and change compatibility mode to Windows 7
Open setup file and re-install
Ta da! It should now work like new.