rcklln
Could be caused by a direct monitor/mix setting with the audio interface

Have you checked this? Aside from crosstalk inside the PreSonus (unlikely), you could have DAW monitoring in your input path.

I'll get to that PC today and try some of these suggestions. Looks like I'll be recording that track again any way.
 
Thanks for the tips so far, guys.

That's such a low-level signal, I think it has to be analog circuit isolation issue. And I found a couple references to this problem with Presonus Firebox on the web:
 
http://forum.cockos.com/archive/index.php/t-44610.html
 
http://www.larriveeforum.com/smf/index.php?action=printpage;topic=23778.0
 
 

It has to be my firebox then! I've tried everything suggested and it still bleeds through. Now I have an excuse to use this old windup pendulum metronome I have.
 
Thanks again for all the info, guys. Greatly appreciated.

That's not good thet your interface has a crosstalk issue. I would test it and if so then get rid of it. If there is cross talk then every track you record will be contaminated with the playback. 
 
To test it, simpley record a new track with nothing plugged in but turn the input gain way up. Now listen to the new track. 

Cactus Music
That's not good thet your interface has a crosstalk issue. I would test it and if so then get rid of it. If there is cross talk then every track you record will be contaminated with the playback. 
 
To test it, simpley record a new track with nothing plugged in but turn the input gain way up. Now listen to the new track. 

 I unplugged the guitar so nothing was plugged into the presonus. Did as you said, turned the gain all the way up, recorded a blank track and as soon as the drums start (ezdrummer2) you hear faint thuds on playback.
 
I also noticed it was very noisy. With nothing plugged in shouldn't there be silence?

I know the Firebox has a mixer. You may have playback, mixer or headphone output set wrong or something. Just a guess.

As Cactus said if you have nothing connected to an input you should only be able to pass silence to the computer. It should only record the noise floor of the device. Noise alone could also mean issues on the playback side, but crosstalk implies the guts of that box are not isolated properly (definitely not good).

How old is that unit?

I bought it 2008. I never really noticed how much noise it produces.
 
Looks like I'm in the market for a new interface...