So I bought this 2020 Acura ilx from auction and fixed everything but this one sound. It runs and drives great with no problems no decrease of power at that specific rpm either, I’ve already replaced the entire exhaust system including the cat and the heat shield near the muffler. It had hit something on the bottom so I know it has something to do with that but don’t know what else to look for, any help I appreciate (it only happens at about 1,750RPMs)

 

It was the vacuumed lines on the car hitting the fuel tank causing the rattle

 

wow, a resolution! thanks for sharing.