'01 LT Loud bang when I hit a pothole

I have an '01 LT and recently when I hit a pothole I get a loud bang (a hard hit that really makes you think you just got hit) as if something is hitting the undercarriage around the rear wheel on the passenger side. I've taken this in to a few places and crawled around under it myself and no one can find anything loose, damaged or even any signs of anything hitting the body.

I replaced the shocks ~5yrs ago and they were pulled off and checked along w/the compressor pressure. The exhaust is fine and not moving excessively and all the lines look fine. Every weld and bushing appear normal and at most a little rusty/worn. I don't have anything loose inside and the spare is tight. I rode in back and confirmed it's just forward of the tire but nothing appears bad on the outside.

Scheduled for the dealer on Monday, but it's driving me & my mechanic crazy. Has anyone ever run into a similar issue? We're starting a family vacation soon and I just don't know if this is safe or if a wheel is going to fly off on the interstate.

What about in the compartment where the jack is stored? Is the jack loose?

Nope. I even removed the jack and rear seats. It still seems to be coming from under the car, but only on the passenger side. Tried hitting the same potholes on the driver's side and no noise.

I'm going to pull the side panel in the rear today to see if there is anything loose in there.

OK, the only thing in there is the power door motor, insulation and the seat belt. This is aggravating.