Ah, but you shouldn't be using a plain resistive heater in most circumstances. Heat pumps are much more efficient.
I've been around dozens of air conditioners, every one quite noisy compared to a resistive heater. Are heat pumps quieter than air conditioners?
Resistive heating is usually much quieter, however it can make annoying ticking sounds as the metal expands against the wall, or an annoying electrical buzz as the power is cycled on and off, multiple times a minute. This happens even if they're installed perfectly, houses and walls move over time.