.noise-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 9999;

  opacity: 0.05; /* регулируй силу шума */
  filter: url(#noiseFilter);
  mix-blend-mode: overlay; /* можно soft-light / multiply */
}