I was backing out of my driveway and I heard this loud bang. I thought I hit something, but it turns out that my Ford Explorer had become stuck in 4wd. I had never even used the 4wd. I didn't think much of it but every time I tried to take a sharp turn it would make a loud banging noise. I didn't get it fixed right away, but it was killing my vehicle. I finally got it repaired but the 4wd lights inside my truck continue to flash. Ford apparently makes the flashing lights difficult for a typical mechanic to fix so you have to take it to one of their dealerships.