: A great source for high-quality field recordings. You can find and download heavy rain and thunderstorm tracks for free, typically available in MP3 or WAV formats.

: A professional-grade library where you can download free nature sound effects instantly in high-quality MP3 and WAV formats. Streaming and Dedicated Apps Free Rain Sound Effects Download - Pixabay

: Offers thousands of royalty-free sound effects, including heavy rain tracks that you can download directly as MP3 files for personal or creative use.

While there is no single file universally identified as "8186 mp3," you can download high-quality, long-form heavy rain sounds for sleep and relaxation through several reputable platforms.