The answer to 'why is my spider scratching sounds' is that the scratching or rubbing sounds are likely caused by the spider's movements and behaviors, not an actual scratching or scraping sound. Spiders don't have the ability to make a true 'scratching' sound, but their movements, especially larger species, can create audible vibrations or scraping noises as they move around their web or environment.
This is a common occurrence and not a cause for concern. Spiders make these sounds as a normal part of their natural behaviors, such as moving around, spinning their web, or even communicating with other spiders. As long as you don't see any signs of an infestation or other pest issues, the sounds are likely harmless and don't require any action on your part.