Engine rattles at start up from cold

Welcome to temperature

If the sound goes away, confirm the oil is clean, full, and not mixing with anything. Next, a lower end noise is more of a knock and not a rattle. Does the sound ever happen after you have been driving? Also, what brand oil filter are you using and what weight oil? Are you located in a hot or cold climate?

Here is a link that discusses common things which can cause a rattle. Your vehicle is older so some will not apply, but there are things that do.

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

Let me know.

Take care,
Joe