Have you had a human curl up in back, in the hatch while you go over an offending bump? I had a friend who had a similar problem and had his wife in back and then he did the same with his wife driving. ( both in 50's) No luck. Then he had his 20 year old son go back and he found it, he could hear better and pin pointed it. It ended up being a large wiring harness connector to the back, behind the rear plastic shell, just hanging at the right point hitting the rear wheel well shell that was acting as a drum, He wrapped with foam and tapped it the wheel well with Gorilla tape.The last few months my 2019 Kona began making a rattling noise in the hatch/back area when I only go over sharp and short cracks in the pavement, small bumps, and shallow potholes. It does not make the sound when going over larger things like train tracks. It sounds more like plastic rattling against something else rather than metal, but I am not completely sure. The rattle is usually a 3-sound noise, like a very fast 1-2-3. Since I noticed the rear windshield vibrates like crazy when I drive under air dryers after a car wash and when other drivers have their bass turned up loud, I thought maybe it was the windshield, so I placed padding in the space between the glass and the plastic around it, both inside and out, but that's not it. Thought it might be the rear license plate, so padded that and that's also not it. looked at the spare tire and the tools, but they all seem pretty snug. I repositioned the back seats and drove with them folded down, and it's not that. I popped opened the small electrical access panels on the inside of the hatch since it did seem like if I pressed down on the plastic there, it made a bit of a small rattle noise, but when I added some temporary padding inside that opening, the rattle was still the same as always. It does not sound much louder when I drive with the windows open, but I really can't pinpoint if the sound is more on the inside or outside. Last month when I took my Kona to the Hyundai service center for a gas tank issue I also asked them to see if they could figure out the rattle, but when I picked up my Kona the dude said it was driven around but no one heard anything. I asked how far it was driven because it only makes the noise in certain conditions and the dude started to act a little evasive. Today I have an appointment at my local mechanic to get the alignment and steering looked at (3rd time in a month after not having any problems all winter - something weird going on there too) and am going to ask them about the rattling noise. I have tried my hardest to find and fix the problem myself. Has anyone else had a similar issue and have an idea of what might be causing that noise? Thanks so much for your time!
Did you check for stuff under your front seats?
Get some Meguirs/armor all interior spray for plastic and go nuts spraying cracks where interior plastic meets everything. All door and hatch gaskets.
On the rear hatch, there are 2 rubber nubs that let you adjust the rear hatch, close height. Extend them. Spray armor all on your lower and upper suspension rear spring seating spots. Pull the rear seat lower cushion, armor all/vasaline the metal tab points.( push the front back hard pull up). Spray the back seat hinges and where the rear seats met the plastic interior. Spray the hatch floor where the plastic interior touches the hatch floor.