The license plate has a great deal to do with who is stopped. California, Arizona, Oregon, Washington, and Colorado are favorite states.
It is assumed if you are in a rental care from one of these states and are a minority and young, you have illegal drugs in the car and they will use any violation to stop your car - speed, seat belt, license plate bracket, etc.
Remember marijuana is not legal in Iowa and you can go to prison for possessing it. Do not consent to a search. Do not engage in conversation. If you are stopped for whatever reason, when asked if they can search, say no. The less said the better. They are not your friends.