I cannot find the reason for the steady high-pitched hissing noise, despite the fact that it’s quite intense.
Can you help me figure it out?
This is my setup (all connected mono):
Synthesizers --> Behringer Eurorack Pro Mixer --> Golden Age Pre-73 DLX Preamp --> Elektron Analog Heat --> Strymon TimeLine (Delay) --> Strymon BigSky (Reverb) --> Yamaha MG 82 CX Mixer --> Yamaha HS-8 monitors
Thanks so much!
What have you already tried to isolate the problem?
Heat ? 
Plug your mixer into your monitors. Any hiss?
From there, just backtrack, keep adding one thing after another til you find out what causes it. Then try eliminating that and see if it stays gone - it could be an interaction between machines.
Also if your heat is connected to a computer, it could be that - try running the computer on battery or with a ground lift plug and see if that kills it.
Yeah, do some trouble shooting…test out 1 device at a time as well as cables…ANYTHING in the signal chain. So far all my noise issues have been cheap audio cables (not saying that is your issue) or having power cords mixed with audio cables. I’ve also gotten a loud wine/hiss from having an ipad on too close to a speaker.