Mysterious Rattle...Any ideas? 2011 Mazda2

Hello Fellow Mazda Owners!
I’m new to the forum and joined because my wife has a 2011 Mazda2 Sport she purchased from her grandmom a few years ago. It’s got 59k miles on it and generally runs like a dream! We’ve both noticed especially on cold start a rattling coming from front passenger side of engine. While warm I noticed it seemed to go away when I cut the AC off? Any well known fixes I should be aware of? Is it a tensioner that maybe needs to be tightened or am I looking at a replacement? I will attach a video of no one knows this as a common issue.
 
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