Apologies in advance for a lengthy post, but a few things to report here.
I received the same message prior to my service appointment and thought it was generous that they offered a loaner (depending on availability) OR $100/day toward Uber/Lyft, so I kept the appointment. Happily, when I showed up, within about a half-hour they put their lead technician, who was very competent, diligent, and understanding, on it. We spent a good bit of time together in my car ensuring he was perceiving the same issue I was and talked a good bit about the nature of the suspension on the car and the general consensus in the forums that it is the rear door that causes the issue (I’m still not sure that is true—I think it may be the “frequency” of energy coming from the suspension on certain surfaces with a certain inherent resonance in the car frame, body, or interior, though rear door movement may exacerbate the issue).
After duplicating the issue by driving my car, we drove another MY of the same configuration (same wheels and suspension MY LR DM), and it had the same issue. Whether it was as severe as mine, hard to say. He showed me how they adjust the rear door and explained the function of the different adjustments. Contrary to what is popularly said in the forums, he said the four rear door “stops,” however tightly they are adjusted, provide minimal rigidity to the door compared to the actual latch, the body-attached rectangular “loop” of which can be moved to adjust the degree to which the door presses down on the seals when it is closed. He explained that to make it more fixed in place, the latch can be moved “down” so that the door closes more tightly against the door seal. Before we adjusted the “loop,” the door stops on mine were already adjusted out to the point that paper could not be pulled out from between any one of them and the door without tearing it. Adjusting the loop to “tighten” the door closure is a game of moving the loop “down” to the point where the door is pulled down further when the closing mechanism “cranks” the door down, but not to the point that the closing mechanism (motor) is not powerful enough to close the door completely. So, I was surprised that he was able to move the loop down significantly without readjusting the stops and the door was still able to close. Thus, the rear door on my MY now closes MUCH more tightly than it did before I took it for service, visibly more tightly, because there is now noticeable misalignment between the door and the body around it, though it is not unsightly because it is symmetrical left and right.
Key question, though: did it help with the irritating low frequency sound? No. Not significantly anyway. Certainly not on roads where it was a noticeable issue before. So I’m not convinced it is the rear door that is the issue.
Next step may be to adjust the door so that it closes less tightly than before to see if that helps. I am curious whether the issue is as noticeable in a performance MY which has a different suspension. I’m also curious whether a different suspension such as an air suspension would help. In any case, I’m surprised Tesla makes a car in which such an issue exists, though obviously the MY is not the only car with the issue — MS suffers from it, too. I’m pretty busy so I can’t dedicate a huge amount of time to going for service over and over to try to resolve it, though I wonder if it could be escalated so that Tesla engineers would have a look at it. I’ll keep you all posted.