The answer to 'why is my silverfish scratching sounds' is that the scratching or rustling noises are likely caused by silverfish moving around and feeding on materials in your home. Silverfish are small, wingless insects that thrive in damp, dark areas and feed on things like paper, fabrics, and starches. The scratching sounds you hear are likely from their movements as they search for food and shelter.
Silverfish are generally harmless to humans, but their presence can be a nuisance and they can cause damage to household items over time. To address the issue, you'll want to identify and eliminate any sources of moisture that are attracting the silverfish, such as leaks or high humidity. You can also try setting out traps or baits to control the population. If the problem persists or you have a large infestation, it's best to call in a professional pest control expert to properly assess and treat the issue.