Fellow broadcast guy here. I've been listening for several hours -- really enjoy your classic rock mix -- and other than ST doing an occasional background noise "suck up" on older analog-recorded tunes (extreme example: what sounds like cue-burn on the intro to Buddy Miles "River"), I just don't hear hiss.
I do notice that your upper highs are... forgive me... a bit high. Maybe it's just that one listener who is sensitive to "tizzy" highs, or just the sound of codec audio, and they don't know how best to describe what they are hearing. Or they just don't like any processing; can't help there
Just my opinion, but I wouldn't make drastic changes for one listener. If you have equalization turned on, maybe back down frequencies above about 7.5K a db or two -- small changes, please. You may also want to look at using or adjusting the noise gate to slow down the processing on the highs.
Stream sounds great, keep it up.