On first start, there is a rattle that goes away after the oil has circulated throughout the engine?

Can you please shoot a quick video with your phone so I can hear the noise? That way I can tell for sure what's going on. You can upload it here with your response. It sounds like the oil needs to be changed, which is what I would do first and use a heavier weight oil than usual.

Here is a guide that can help:

https://www.2carpros.com/articles/rattle-noise

and

https://www.2carpros.com/articles/how-to-change-engine-oil-and-filter

Please go over these guides and get back to us.