I literally had the exact same issue with my ‘21 Trailhawk…same noise, same speaker (upper small speaker on rear passenger door) same Kenwood audio system, only made the noise when the taillights were illuminated (brake lights, turn signal, taillights being illuminated with the headlights). Mine took almost 3 weeks to fix after getting Chrysler techs and a Star case opened. The dealer first thought it was a blown speaker and tried replacing them without success. The diagnosis ended up being a short somewhere between the rear passenger door and the taillights that caused the buzzing noise. The dealer ended up ”overlaying” new wiring over the factory wiring to get rid of the issue. They could never find the actual short, but overlaying the old wiring bypassed the short. This came from the factory this way…had the problem from the first miles on the truck. Once the problem was fixed, the buzzing noise was gone, but the speakers never sounded the same, not sure why. That was only one of many issues I had with my Renegade and eventually it pushed me to turning my lease in just 8 months in. I was convinced that I had a Friday-built Jeep, but it sound like they could have a manufacturing issue with that audio system. Best of luck…don’t let a dealer tell you that you don’t have an issue.