Roaches can randomly poop anywhere. However, most of the time their smears are near their nesting or hiding places.
Roaches that infest homes don’t make sounds audible to humans, but roaches crawling inside the walls can produce a chirp that at times is audible to humans. That happens when there are many roaches or an entire colony of roaches hiding in the walls.
You should also seal off any entry points that allow roaches back into your home. Check around doors, windows, and utility pipes for cracks or openings where they might be coming through. Make sure that all food sources are kept sealed tightly away in containers with lids on them, so they don’t attract ants as well as roaches, and contact a professional if you feel the scratching in walls continues after your treatments.
