[daeron80]

Track menu > Input Only Monitoring
Windows shortcut Alt+K
Mac shortcut Opt+K

The reason it goes silent is because it's playing the audio on the track (whether there's actually any there yet or not). To hear what you recorded on that track, you'll need to either switch it back, to normal monitoring mode, or take the track out of record arm.

You know, I never thought about it before, but it might be kinda cool if PT automatically monitored the input of record-armed tracks whenever there was no audio region present. Eh? At least an option to have it do so. As you played along, you would hear your input until you got to an audio region, then it would automatically switch and play that region, and when you reached a "clear" area, it would automatically switch back to input. Why not?