02’ Explorer. When I put it in reverse going straight back it doesn’t automatically start to roll. When I give it gas there is a grinding noise and it feels like I’m running over something and then it rolls smoothly.

When I have to turn the wheel while reversing the grinding last a little longer.

What’s the issue?

 

The 5-speed automatic transmissions in the Explorers (as well as a few other models) are known for shift solenoid issues that effect reverse. You're probably looking at needing a new shift solenoid and possibly needing to have the case drilled and sleeved to fix the issue. If there's a transmission shop in your area that you trust, they can likely give you a pretty accurate estimate to repair as they've probably done several.

-Rod