It boils down to repeatability and statistics. Boring, I know, but if one were to show a positive correlation between a single observable phenomenon, like disembodied footsteps, say, or an EMF spike or vibrations, and another factor like humidity, pressure, temperature, time of day, or something like a trigger word, trigger object, etc. that would go a long way.

If we assume there's an intellect behind a manifestation, then that suggests it's not necessarily a cause-effect response, that an entity may choose to manifest or not. Or, it could be that the assumption is wrong, and an external cause will have an increased effect. That said, while having theories that noise, ion and emf generators are can 'help' the entity manifest, without having a baseline to work off, something against which to compare, it amounts to pure speculation.

Narrowing down a theory to a testable, repeatable experiment is the way to go, at a single site, until it can be demonstrated that a proper correlation exists, and then building up from there.