Why is my car rattling under the front of my car

What is your question?

Every time I start my car I hear a rattling sound under my hood I can drive I don’t hear it and sometimes it goes away but every time I start my car periodically I hear rattling

What makes this problem better or worse?

It is worse when it’s cold

How long has your 2015 Nissan Sentra had this problem?

Two weeks