So, I tried:
Eheim compact 1000, noisy and heat the tank to 30C.
MJ 900, noisy.
Sicce Syncra 1.0, noisy.
Stock pump, less noisy, weak and easily clogged.
Every AC pump that touch the chamber walls creating vibration noise.
Now I found the one and only silent pump: Jebao DCA1200. And no, it wont fit the Fluval 13.5 by default. You need to trim the plastic the the saw, 2 min job:
At the max power the pump is noisy, but after reducing its power via included controller - its a absolutely silent pump. Even at minimum its a pretty powerful pump.
Now I can sleep near the tank without turning the pump off.
Eheim compact 1000, noisy and heat the tank to 30C.
MJ 900, noisy.
Sicce Syncra 1.0, noisy.
Stock pump, less noisy, weak and easily clogged.
Every AC pump that touch the chamber walls creating vibration noise.
Now I found the one and only silent pump: Jebao DCA1200. And no, it wont fit the Fluval 13.5 by default. You need to trim the plastic the the saw, 2 min job:

At the max power the pump is noisy, but after reducing its power via included controller - its a absolutely silent pump. Even at minimum its a pretty powerful pump.
Now I can sleep near the tank without turning the pump off.