white noise in guitar amp sims

Im recording guitar direct into an Mbox 2. The clean signal has no noise whatsoever, very quiet. But when I enable an amp sim such as the Sans-amp plug in or Guitar Rig 5, there is an audible white noise in the background. Noise gates cut the noise out during pauses, but when its playing back, you can hear it. Its driving me bananas. Any suggestions? Anyone else ran into this problem? I thought direct recorded guitar would be super clean.