Not sure if this is mentioned in the manual, but was wondering if anyone happens to know how to mute the sound on the nav unit.

 

There is an adjustment for the volume of the nav unit in the PSM so I'm sure you could just turn it down very low if not off.

 

If the 991 PCM unit works the same as my 997.2, push the "MAP" button during route guidance. This will cause the lady to repeat the last command. While she is talking, turn down "her" volume using the left rotary, volume ****. It goes all the way down to zero on my car.