The FT-991 has two microphones: the front microphone and a rear (data) microphone. I have seen others on the web describe how you have to change menu settings each time you change from SSB to a digital mode so that the microphone will change from the front to the rear.

Using the menu settings found here, you can switch seemlessly between SSB, FM and digital modes without having to change the menu settings each time.

With the above settings, change modes like you normally would.

1. In USB, the mode indicator in the upper-left corner of the display (next to the frequency) will show USB.
2. Push the MODE button.
3. Select DATA-USB on the touch screen.
4. The mode indicator will now show D-U and the rear microphone will be selected.

1. Push the MODE button.
2. Select DATA-FM on the touch screen.
3. The mode indicator will now show D-F and the rear microphone will be selected.