Rattling noise in dirtbike engine?

I posted here the other day and I'm back with new info and updates.

I did an oil change that didn't help, the oil was low so I was hoping that would fix it

I don't know what it is, its in the engine though, I uploaded a youtube video so you could hear it, the metal rattling sound isn't as bad in real life as it is in the video but the camera picks it up easier but it makes it easier for the camera to hear.

Please help, what the issue is or could be thank you

Added (1). Also dirtbike is a 2009 Honda Crf100F

There's something in the muffler that has broken loose.