Okay but E.A. recounted somewhere that he was doing evocations, and he saw and heard nothing in terms of phenomena, but later found out his neighbours, who weren’t involved and were presumably not even trained, heard banging noises that he couldn’t even detect.
So, possibly this happens for some reason, and maybe outside observers who aren’t even in the region of thinking to look (or listen) for manifestations, CAN pick things up.
Just make sure to banish and maybe see about creating some wards: What's normal? (Creating Wards Walk-Through Tutorial)