make sure in the render settings in the 'sampling' section the samples value isn't placed too high, because that value is different from the preview value. setting the value too low will add a lot of noise to the image, but setting it too high takes too long
trying cycles render, that is much slower and/or noisier, (about 13 seconds per frame, and still too much noise, that's at 64 samples) and the viewport is noisy/slow, that would be at 32. Eevee is much faster for both, and with eevee, the preview-viewport version displays absolutely perfectly at 16 samples, absolutely instantly, noise free. And yet, render still takes 1/2 second per frame, at 16 samples. much much better than cycles, but the mystery still persists as to what should stop me from just screenrecording the viewport for perfect instant results ....... and yet the render still needs to compute .... To push this mystery a little bit further, still on eevee, i've set the render sample rate to 1, (!!!) the render still is completely noise free and looks great, (???) and does about 3 frames per second. The viewport preview, however, i've just set to 500 samples (!!!), and it still renders absolutely instantly. ?????? it's got to be aliens