Transmission will not stay in park and makes a loud noise when driving

Can you get a recording of this noise? Is it a loud ratcheting type noise?

The first place to start is to check the fluid and find out if there is metal in the fluid or what the condition is.

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

The fact that it won't stay in park points to a park pawl issue.

This is basically what is used to lock the output shaft so that it will not move or roll away when it is in park.

So, I would suggest we start with getting a recording because this makes a distinct noise, and we can go from there.

Thanks