Yes, mild hiss is normal, especially if you're going into an amp that's being overdriven. In my experience with the electric mistress, she is a finicky bitch. She just doesn't get along with certain pedals. I've built the current lover and old chap, and both of those pedals didn't get along with analog delays in front of them. They also didn't get along with a Digitech Drop. This hiss that accompanied the sweep was louder than the effected guitar signal with the drop engaged. The only thing I found that helped with my noise issues was having a buffer at the beginning of my signal chain. Even with that, I still had issues when using the Digitech drop. Ultimately, I ended up ditching the use of the mistress because of these issues and went back to using my trusty bf-2.