This happens to me constantly and I've never heard a good explanation for it. Before we even start the session properly, sometimes before we've even set our intention, the recorder just goes haywire with static for maybe 5-10 seconds then settles right down.
My mate Karen reckons its the equipment "warming up" to the environment but honestly I think theres something more to it. I've started treating it as a signal that something is already present and paying attention. Like the energy in the room shifts and the device picks it up before we do.
What I'd love to know is whether people get EVPs in that pre-session static when they review the recording later. Because I have, twice, and both times it was a voice that sounded like it was trying to get a head start before we officially began. Caught me completely off guard the first time.
Anyone else actually gone back and listened carefully to those first few minutes rather than skipping to the formal session? Worth doing if you haven't.