[jnmarshall]

The HK/NAV unit for 2017 (and possibly 2016) has its own manual that is separate from the general manual. Pages 99-101 of that manual refers to an "Automatic Sound Levelizer" that appears to function as a speed sensitive sound adjustment, but those functions don't appear in my unit (they are grayed out).

The ASL or Auto Sound Leveler is to adjust volume from other sources of input to match the tuner(Am/FM). It's greyed out when using the tuner to listen to AM/FM. If you switch to another source like USB or BT it will be available. If you find your BT input for music too quiet or too loud you can adjust it with the ASL to be at a similar volume level as the tuner.
I'm disappointed too that it have a speed dependent volume option. Sometime called SDV or SDVC or SDVL found in other cars.