Yeah this has happened to me a few times. Was doing a session in my flat last year - old tenement building, loads of history - and you'd get this weird burst of static almost like a warning shot before anything came through. Happened consistently enough that I started treating it as a cue to pay more attention.
Not sure if its the spirits actually causing the interference or if both the static and the contact are being caused by the same underlying energy shift, if that makes sense. I lean toward the second theory but honestly I dont know enough about the technical side to say for certain.
Anyone actually recorded the frequency of these bursts? Curious if theres a pattern. I've only got basic kit so I can't analyse it properly myself.