A bit late to the party and I hope you were able to figure it out but now, drisley, but in case there is anyone else who ran into this issue as I did, this is how you enable audio levels during video recording.
Go into Camera Settings > Page 1 > Sound Recording
Make sure sound recording is set to manual.
Now, as long as you aren't shooting in 120 fps (since 120 fps doesn't record audio levels) you will be able to see and adjust your mic recording level straight from the shooting screen.
If you don't see it, make sure you use the info button to scroll through your different info display modes until the shooting info on the sides of the screen show up (AF; Recording format; AWB; etc)
If none of your screens have it, Go to Menu SET UP (4th top box) > Page 4 > Shooting info. disp > Screen info. settings
Then just edit a screen to include detailed shooting info.
Hope this helps someone out there!
-FiveAces