Guitar hiss????

hello all,
 
Im trying to get my guitars to be as clean as possible and am at a loss. I hope that someone here on this forum could lend some advice and possibly trouble shoot.
 
My interface is a focusrite pro 40. I am recording guitars direct. Guitar- cable - interface.
I record all my guitar tracks and everything sounds clean. After the recording is done I start with the editing of the track. The reason for recording direct is so I can use pod farm as a vst plug in and generate whatever guitar tone I desire. I noticed that when I put a guitar pre amp on the direct signal, hissing shows up in the back ground. It left me stumped because I thought the signal sounded clean whenn I originally recorded it direct. So I figure it was just the pre amp I was usinng in pod farm and I proceed to try a different one, well long story short, it seems no matter what pre amp I put on the signal the hissing still pops its head out. 
So, I started from the source to see if maybe there was some kinda bleed. I proceed to take all plug ins and EQs ect ect off of the the guitar track so I could hear the direct signal clean with nothing on it. I turn the volume to a high level to focus in on the guitar track and sure enough there is a faint hissing in the back ground. How could this be????
Everything is being recorded direct. Could it be the guitar pick ups?
Its not noticeable at all, until you turn the guitars up high and listen for it, but its there. So, I guess when I started the editing process and cleaned up the signal is when it starts to become more apparent that its there.
Ive tried using a noise gate, EQing, turning the treble down on whatever pre amp im using and nothing seems to help. Plus when I do these type of things it takes away from my tone.  Im at a loss and after hours upon hours and days, I turn to you gentlemen for some assistance.
 
Please tell me what I could be doing wrong. Should I be using a DI box? My interface is really good and should be able to handle this without a DI.
 
If nothing else I could really use some tips in tackling guitar processing. Step by steps would be really helpfull.
 
Thank you very much for any help you guys could lend.
 
-Vokalzz