Alright, so there's a place in a track I'm working on where any MIDI notes I draw there in the piano roll are either muted or they are shown white and don't play any sound.
What is happening here? I've had this before and I'm not sure how to get past it... is it some sort of 'mute zone'?

Did you by change use the mute tool? 

Maybe the result of the recording mode; to unmute a clip, select it use the keyboard shortcut "K" or right-click to bring up the context menu or use the comp tool in the track lanes.

Mute tool has no effect! It's a section of only about 4 beats long and I *think* it happened at some point when I recorded audio there. If I bring the mute tool to it, I see a red circle with a line through it.

I am pretty sure if you have take lanes with midi the ones that aren't in the comp show in piano roll view as muted. I think if you collapse the take lanes it will just show the unmuted ones, I will go and check it out and come back.
 

Yep if you comped the midi track the unused notes show as muted. when you flatten the comp and delete muted takes they go away.
 

davdud101
Mute tool has no effect! It's a section of only about 4 beats long and I *think* it happened at some point when I recorded audio there. If I bring the mute tool to it, I see a red circle with a line through it.

Mute tool mutes if used in the lower half of a clip, and unmutes if used in the upper half (icon changes to a square).
 
 

Make sure that the clip where you are drawing in new notes actually covers the area you are drawing in, you may need to extend/move the clip boundaries.