I am using a RODE condenser "studio selection" microphone to record Classical guitar. I am using it with presonus firebox on garage band. The reverb effects and all sound great, but I get this hissing sound in the background. Is this normal, or do I need to do something to eliminate it. I was thinking about trying to record in the bathroom where the acoustics were better, just kind of a pain to set up there. Any advice would be appreciated

If the hissing is not background noise (noise from your house), then your most likely culprit would be that you are pushing the pre amp for the mic to hard. Back off of the gain and see if that helps.

I dont know anything really specific about your gear.

Have you checked out the impedance and level-matching
between the Rode condenser mic and the Firebox?
( these values may be switchable on your gear )

AS an example:
Connect a low impedance load/input to a high impedance driver/output
and you can easily overload and shortcircuit the high impedance output.

Cheers: Dixiechicken