what do you mean by “metallic sound”? you mean like this?
https://www.youtube.com/watch?v=JtBiY2sPNJ8
I would return it and get a new one or get a different brand speaker (this is a common issue with JBL speakers, from what I see in my internet research).
if you decide not to return it, open it up (when you do, it’ll be harder for you to return it!). check the speaker wire connection to the speaker terminals - from personal experience, it’s probably a loose connection (i.e. you’ll have to resolder it) .