Dropbox, Google Drive, or a personal web server are popular options.
Just make sure you have a link directly to the raw file. Many of the online hosting services link you to a webpage with a preview of the file.
Dropbox
On Dropbox you’ll want the URL to have ?dl=1 at the end. For example:
https://www.dropbox.com/s/yzlcva03b6dquxy/Alien_Siren-KevanGC-610357990.mp3?dl=1
Google Drive
For Google Drive it’s a bit more complicated, but there are a bunch of sites online that will convert the URL for you. (eg. https://www.gdirect.link/)
When you get the shareable URL, it will be in the following format where XXXXX is the document ID:
https://drive.google.com/file/d/XXXXXX/view?usp=sharing
It needs to be in the format:
https://drive.google.com/uc?export=download&id=XXXXXX