Don’t think your going to find a good heater that doesn’t click. That’s just the relay turning on and off. Without it, the heater will stay on or off. If you want, you can get an InkBird controller and set the temp differential to 2-3 degrees. It will let the temp in your tank fluctuate a little more, but the heater will go on and off a lot less.
Ive never noticed any that do click. If it's audible it's too muffled by the water.
Are you talking ones with the separate temp controller outside the tank?