when i change the nav. volume in the settings menu it appears to operate normally - saying "softer" when i turn the control one way, and "louder" when i turn it the other way - but the volume never actually gets very soft.

Despite being set to the "softest" setting in the settings menu, once I use the navigation system, the instruction volume is very loud.

When the navigation system gives an instruction, turning the volume control knob during the instruction will lower the volume of that instruction. If the stereo is also playing, it will also lower the volume of the stereo.

The next Nav instruction will be at the original loud volume, whether or not the volume control was adjusted again after the first instruction.

The volume control works normally for the stereo at all times.

Hope that is clear.