Help with hiss

Man, I am so appreciative for all these suggestions and help! I knew I came to the right place!

@erik_squires As far as the LED thing, this is a large kitchen ceiling light that I converted from 2x4’ fluorescent bulbs to 2 LED bulbs. I didn’t replace the fixture, but bought the LED’s that have the built in ballast to be able to operate them in the same fixture. I’ll replace the entire fixture when I find one I like. So, no strips, wall warts, etc. And they are not dimmable. Like I said, the hiss occurs whether or not that light is on.

The WiFi modem/router is in the same place it has been for years (20+). It’s also the same one I’ve had for years. I did eliminate it on the off chance that it was creating a problem, but the hiss continued. 
I may have to shut down the whole house to find this. I am not opposed. Thank you!

@soix I can’t argue that the Mac is less than ideal. I was an early adapter of Roon and, at the time, the options were pretty thin. The Mac was something that could run Roon and I was familiar with them. My next upgrade is a real streamer, so the MacBook’s days are numbered. Even so, I’ve had this configuration for years. The only thing this Mac does is run Roon. It is the only thing it has ever done. I have never used it for any other purpose. I did unplug it from the Brick Wall ( those wall warts can be problematic), but the hiss continued.

@carlsbad2 I will unplug the outputs from the preamp. Good idea. Power and one input (from the preamp) are the only things plugged into the amps. I, too, fear that this is less system related and more power grid or power supply problem (from outside). That makes it beyond my control which I don’t want to think about right now.

@oddiofyl I don’t have anything like that. I’m hard pressed to remember that last “new thing” I introduced to this house. I’m not a big change person. I research the life out of something, make a decision and then live with that decision until it breaks or becomes so outdated that it no longer serves a useful purpose. That’s why this is a little baffling….nothing has changed, but the system suddenly began to exhibit this annoying feature. Thank you!

Assuming it's NOT your equipment, did you replace interconnects in that period of time? If you went from unshielded to shielded that would explain general noise pick-up but weird if it's hiss specifically.

@erik_squires I had that thought as well. I didn’t so much change any cables, but I did add a cable around Christmas time. I got a Schiit Loki for Christmas, so I broke out a pair of Raven Audio cables to use to put the Loki in the system. Unfortunately, right now, I have a hodgepodge of cables and not a full loom from one manufacturer. I have mostly Audioquest, but a couple of Zu Missions (I think), and the Raven. My turntable is a Rega, so the cables are captive. 

OP:

Well, I don't mean to suggest any cable brand is particularly good or bad, I was just wondering if you'd made a change that could account for it.

Right now it looks like you have to go up the food chain, but keep en eye out for any wall warts.  They still generate noise even when the load is off.

A couple of things to try.. first, re-route all cables making sure that the low level cables (interconnects) are at 90deg to any power cable they need to cross. Make sure speaker cables are kept away from power cables.

If that doesn't help, turn everything off, disconnect any interconnect to the mono blocks and then turn them on. If you still hear the hiss, then it's from the amps. If you don't, then connect the interconnects but do not turn on the preamp. If hiss, then it's the connection (interconnects or the input of the amp). If no hiss, then connect the preamp (test first without it on and then with it on). And so on, work your way backwards until you identify the source.

I went through this exercise only to find that if I plugged in my integrated amp to a different outlet on my PS Audio PowerPlant, any and all hiss went away.