Update - email I received from LexusI just came back from the dealership and they removed the rear door panels and showed me the "dummy" speakers in the bottom set of speakers in the rear doors. They claim that this is how it is supposed to be and said that another Lux+ with ML also had the same setup. The speaker map shows that they are speakers in that location.
Lexus dealer technicians are specialized in the diagnosis and repair of Lexus vehicles. They are provided with extensive training and have access to state-of-the-art equipment to accurately diagnose and repair your Lexus. As such, we concur with the diagnosis provided by your servicing dealer.
Additionally, we have looked further into your concern with a product specialist and our records indicate that the third speaker has a box assembly. This means that it outputs the noise reducing sound to reduce noise and does not operate as a normal speaker.
If you feel you need to discuss this matter further, we kindly request you to please call the Lexus Brand Engagement Center at 1-800-255-3987 and provide your reference. Any representative will be able to assist you. Our hours of operation are 8:00 a.m. to 8:00 p.m. Eastern Time Monday through Friday and 9:00 a.m. to 7:00 p.m. Eastern Time on Saturdays.
Sincerely,
Ivan
Lexus Brand Engagement Center