Why would I be hearing a rattle when my speed get up to 1500 rpms

What is your question?

Once I start it in the morning there is not problem. As it get warm and traveling at 1500 rpms the rattle starts and stops when I push the gas. Only happens at 1500 rpms under load

What makes this problem better or worse?

Not rattle over 1500 rpms

How long has your 2017 Cadillac XT5 had this problem?

a few weeks