A transparent noise overlay lets you add texture to several designs without baking it into each background. The useful part is control: color, blending and opacity can be adjusted later.
Export the right layer
Create a noise texture in NexTools Grain & Noise and choose a transparent PNG when the available settings support it. Confirm the download really contains alpha transparency by opening it over a checkerboard or contrasting background.
Blend it into the design
Place the PNG above a gradient or photo. Try normal opacity first, then compare an appropriate blend mode in your editor. Look at smooth areas for banding and at detailed areas for visual clutter. A large overlay should be exported at a suitable resolution rather than stretched from a tiny tile.
Save the working file with separate layers. That makes it easy to reduce noise for text-heavy layouts or reuse the same texture consistently across a series.