Echo Audiofire users

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I use a sm58 for recording vocals (in an apt., condensor picks up too much noise), and I have to use a preamp before entering the Echo Audiofire 8 to obtain decent levels. I use the universal inputs for vocals, therefore it goes thru Echo's preamp (set low) also. When I use the universal inputs, I noticed a strange thing. The software console shows that the track input is picking up noise even when the microphone is turned off.
What would cause that? All my cables and connections are balanced. I read in the SOS review about the Audiofire where they mention something about ultrasonic background noise being a by-product of the Cirrus Logic Convertors (uses infinite impulse response filters).
I don't know if that has anything to do with this, but does anyone have any thoughts?

Thanks,


P.S. I agree with some of the other postings about these units that the driver is very stable and to me the sound is pretty good.