If you have a hitch ball mount installed, that thing can make a very annoying rattle when going over the smallest cracks on the road, especially at slow speeds. The sound is hard to trace, since it travels through the frame once this heavy piece of steel starts rattling in your hitch receiver. I was chasing this notice for a while until I realized what it was. Aside from the obvious things to check like front body mounts, stabilizer bar bushings and end-links as well as loose skid plates, there could be a few more culprits that I found were making noises under the hood:
1. Hood support - that stick is simply loose and rattles all over the place.
2. Transmission vent hose - this hose comes up from tranny and end behind you airbox. It's secured tight on the very top, but grab it and wiggle it around half way up - it makes some nasty sounds.
3. AC lines on the firewall (engine compartment).
4. Steering shaft - make sure the first connection where he saft comes out of the cabin is tightened properly. Just tug it a few times to make sure that bolt is tightened all he way.