2004 Honda Pilot drivetrain & axles problems

I was parked in the driveway on a completely flat surface. I put the car in reverse to back out of the driveway. I touched the accelerator pedal lightly to get the car moving, the car accelerated wildly. I stomped on the brake, which went to the floor. I had time to look down and see that my foot was on the brake pedal and to stomp on the emergency brake. The car did not slow down at all. The vehicle continued accelerating until it smashed into a tree going approximately 30 MPH (estimated).

While driving to the airport for family vacation, my 2004 pilot started making a grinding sound every few minutes. When we returned 2 weeks later while driving around town between 20 and 40 miles per hr. It continued making same grinding sounds. Had my mechanics look at it suggested changing transmission fluid and differential fluid, did so but it kept on making grinding sounds.