I must admit, I've never used the EQ. I balanced my system using the auto setup and that was good for me.
My question is, how audible is the difference in noise? I mean, every device in the signal path contributes to overall noise. When the EQ is engaged, your directing the signal path through the additional EQ circuitry and, most assuredly, you're going to increase the noise factor somewhat.
But is this increase even audible?