2021 AMG CLA 45 S Digital White w/Performance Package
A quick update, after two days at the dealership and several drive around sessions with the tech trying to pinpoint the issue, they appear to have solved the problem. I didn't get a copy of the job report (as they have left it open pending my feedback) however the SA advised that there was 'excessive gaps between elements that are within the door panels' which they believe to be the issue. They used the silicone and MB sound proofing tape to fill those gaps (in two of the four panels) and on driving home, it does indeed appear to have been fixed. When I got the car I was despondent that there was no longer a 'Mighty MB Gap' in the new model, however, now I am very happy, as they have shifted the Mighty Gap to inside the doors, it is still there, just no longer visible...