Thanks Joestue, you seem to know what you're talking about, unfortunately I dont,,, it's all a bit too technical for me. I'm the original poster of this thread. I have a Trace C40 controller using a Ohmrite
PFE5K1R00E 1ohm power resistor. I'm dumping about 500w into it at 28V. The noise was about the level of the average person talking, so I removed the ceramic core from the resistor and that made it quieter but now it's like having bad tinnitus all the time, a very high frequency noise, I've put a small fan blowing air over the resistor core to try and hide the high pitch noise but it doesn't help much.
I'm almost at the point of giving up on air resistive loads, I dont want to heat water so I'm now thinking about converting an oil filled radiator to a 24v immersion heater, any reason you can see that that wont work or be quiet for me?