So I've been trying to not be paranoid, you know, freaking out about every little sound. So for about 2 weeks my '05 Taco has been making an odd clunk when I first shift in to reverse (it's an auto) to back out of my driveway. It does have a slight slope but not much. Today it has begun to do it when I park too, but does not do it until I shut the truck off. Where to start.