Help with hiss

So, for the LED thing, dimmable LED lightbulbs seem to be OK but some LED strips and power supplies are not. If your LED lights have a wall wart, that may very well be a cause.

Another potential issue is if you've moved or introduced a Wifi router or device around your stereo recently. 

One experiment you might find is to literally turn off everything else in the house from the panel. 

If turning all of that off does not improve your issue then it's definitely in your audio chain.

Wait.  You’re using a Mac laptop as your streaming source???  That’s awful.  Let’s do this — share your WHOLE system from soup to nuts and let’s attack this piece by piece.  The more we know, the more we can possibly help.  Now I’m thinking your streaming source could be part of the problem.  Tell us as much as you can about your system.  The more we know, the more your chances of getting help and finding a solution.  Pretty sure I speak for all here that we’d love to help you solve this infuriating problem, and there are a whole bunch of us here who’d like nothing more than to help you overcome this because we all feel your pain.  Help us help you. 

Unplug the interconnects from your preamp.  that will rule it out.  is there anything else plugged into your amps (besides power)?

If it is still there, then it is likely a power or interference issue as Erik has described.  It can't really be any of your equipment since the likelihood of the same problem happening in both channels at the same time is astronomically small.  Or would that be particle physics small?

I had a weird noise coming from my mono amps a few years ago.   Took a while to figure it out.   It was  plug in air freshener,  every time it cycled to dispense the scent my speakers would make a weird crackling noise.