I recently shared a song I made on the music composition site called BeepBox via exporting it onto scratch with an MP3 file. I am curious if I am allowed to put a link to the version of the song stored on BeepBox.

It must respect: https://scratch.mit.edu/community_guidelines/
So there must be no way to communicate with anyone else privately, or even with the site maker, if the creator of the site is a Scratcher. Plus, it must have no browser extensions linked or mentioned and the website must comply with all current Scratch Policies.

Yes, since it has no extensions, no personal info needed,and no private chatting or anything that breaks the terms of service . And respects the community guidelines.

Be safe: keep personal and contact information private.
For safety reasons, don't give out any information that could be used for private communication, in person or online. This includes sharing real last names, phone numbers, addresses, hometowns, school names, email addresses, usernames or links to social media sites, video chatting applications, or websites with private chat functionality.

Yes, you can link to Beepbox.

Beepbox is fine. I have a bunch of Scratch friends and we all share beepbox links with each other.

In general, it's best to stay away from external links unless you're sure they follow the Community Guidelines- so no private chatting, no personal info sharing, no video chatting, no social media links, etc.