Well, here is my 2nd post on this forum as I've been reading for some time since acquiring my 2008 TL Type S. As the original owner, this vehicle has been cared for meticulously and currently has 40K miles with zero modifications. That said, a very annoying rattle came about over a month ago and it sounded like a piece of wire hitting a bare metal surface. Very noticeable from 15 - 45MPH. I took the trunk lid cover off and zip tied one section of the trunk release cable near the right trunk hinge that had more freedom of movement and could have caused the rattle. No, that wasn't it. The wiring harnesses for the backup lights were also secured but that didn't solve it either. The search continued as I put thin 1/8" thick styrofoam insulation padding under the trunk mat and anywhere it could make any sounds hitting the bare metal of the trunk floor where the space saver tire sits. No luck.

Had to get the car to the dealer for them to diagnose. After several hours of test drives and removing the rear seat and the speaker shelf assembly, it was found that there was some type of metal to metal contact under the driver side speaker shelf. The mechanic applied "EPT Tape", tightened fasteners in the area and was able to resolve this rattle issue. I had asked if Loctite was used on the fasteners and was advised it was not necessary. As I didn't see exactly the location of this problem and how it came about, I can only deduce it was poor manufacturing as this should not have ever occurred.