I am trying to achieve this noisy background behind the cards. How can I recreate this effect?
I'd go with a simple tileable texture that you can expand or contract as needed. It's easy to repurpose that way and doesn't eat much disk space.
Try SubtlePatterns.com. Atle Mo creates and curates a very nice set of patterns there, some of which would work perfectly for this task.
Take a photograph of a concrete slab or purchase a photograph of concrete from any number of stock photography sites.
There's no reason to spend time and effort to recreate something if a simple photo will work. Often the photo works better anyway.