Update...I haven't been able to reproduce the circumstances that caused the hiss. It's been so damn cold down here that my amp fans aren't coming on. I jammed for an hour listening to Pink Floyd, and nothing. Just perfect sounding music with absolutely no noise. I even had the heater going. Maybe tomorrow...LOL.

I'm convonced that the fans are what caused the hiss sound. Once I can verify this, I'll move things around a little to isolate the amps.