I'm not with Laminar Research, just a fellow simmer in the UK.
1. All of the sound .WAV files for weather are in the C:\X-Plane 11\Resources\sounds\weather folder. In my 11.32 version of X-Plane, I have 10 .WAV files covering rain, hail, thunder, wind etc.
Are your files all present and correct as per the following photo?
2. If you have to run the X-Plane Installer app, double click the relevant file in the X-Plane 11 root directory and follow the instructions. You will find the X-Plane Installer app in the C:\X-Plane 11 folder, as per the second photo below.
Hope this helps for now :-)