Yeah this is something I've been tracking for a while actually. Got maybe 30+ hours of recordings from sessions I've done down here in Cornwall over the past two years, and the static burst pattern is genuinely consistent. Not random noise either - it spikes, drops to near silence, then the response comes through in that quiet window right after.
My working theory is that whatever's producing the EVP needs to essentially "push through" some kind of energetic resistance first, and the static is the byproduct of that process. Whether thats electromagnetic interference, psychokinetic disruption of the recording medium, or something else entirely I honestly can't say with confidence.
What I'd want to know from anyone else seeing this - does the burst duration correlate with the clarity of the response that follows? In my recordings there seems to be a rough inverse relationship there. Longer burst, cleaner response. Make of that what you will.
Would be worth people logging the exact timestamps and durations if they havent been doing that already. Patterns don't mean anything if you haven't got the data to back them up.