Yeah, this happens to me constantly and I've never seen a satisfying explanation for it. Been recording in and around the Durham area for about twelve years now and the static burst thing is so consistent it almost feels like a warning that something's about to come through. Like the signal has to fight its way in or something.
What recorder are you using? I've had it on three different devices so I stopped blaming the hardware a while back. One thing I did notice is the bursts seem longer before clearer responses, which makes me wonder if there's some kind of correlation between the duration of the interference and the quality of what follows.
Has anyone actually tried measuring the burst length and comparing it to EVP classification? Class A, B, C etc. Feels like someone should be running proper data on this rather than just anecdotal accounts. Or maybe someone already has and I've missed it.