I'm going over my previously done translations to see if any need further editing, and the following comes up.
I relearned yesterday that a relative clause/qualifying phrase is made by placing a verb or adjective in front of a noun in Japanese. In the above, the relative clause would be 背後で聞き覚えのある. The noun being modified that makes up the main clause is 声.
The issue is that https://jisho.org/search/ある says that ある is both a verb and a pre-noun adjectival, both of which, to my meager understanding, would work in the above sentence to form a relative clause. How do you know if ある is a verb or a adjective in the above sentence?