My dealer seems to think it is speed sensitive - he said it is connected to the same module? as the spoiler. I am having a problem with the volume changing -mostly at low speeds. They have tried to find the problem but it is intermittent so they couldn't diagnose - too late for warranty anyway but thought I might get them to buck up since I just bought it in November. wouldnt cover the seat heater either - love the car but glad that I have the powertrain warranty left. Hopefully I won't need it.