Noise reduction showing no change at any zoom

I’m using RawTherapee and none of the noise reduction sliders make even the slightest difference, no matter how far I slide them. I’ve tried it at all different zoom levels, including 100% (the one I’ve read is necessary to actually see the change in the preview image). Not sure what to do. It’s a very noisy image, so you’d think it would produce some change at least.
Any suggestions?