Your Model S has a coat hanger on each side of the vehicle above the rear window in the second row, next to the reading light. Push the coat hanger to release it. Push it again to retract it.
Active Road Noise Reduction
Model S is equipped with Active Road Noise Reduction which reduces low-frequency road noise while driving on rough surfaces. To accomplish this, the vehicle uses the seat microphones to measure noise in the cabin, then generates anti-noise through the speakers to intelligently create quiet zones around each occupant depending on vehicle and environmental factors.
To turn Active Road Noise Reduction on or off, open the Media Player and touch Audio Settings icon > Options > Active Road Noise Reduction (the audio settings icon shows an equalizer with three vertical lines). This may require several minutes of driving time to calibrate before enabling.
NOTE: To ensure active noise reduction operates effectively, avoid covering the microphones (with seat covers, etc.). Active Road Noise Reduction may disable if a window is rolled down, door is open, or the fan is turned up.
CAUTION: To prevent damage to these microphones when cleaning, do not over-saturate the area of the seats where the microphones are located.