Yeah this is something I've noticed a fair bit doing sessions at various locations around the Midlands. The static seems to come in waves just before you get anything coherent, like the signal is building up or something. Had it happen at a site in Coventry last year, few seconds of heavy interference then a really clear class A EVP right after.
Wondering if its the equipment responding to some kind of EM fluctuation or if there's something else going on. I run a zoom H5 with an external mic so its not a cheap setup, the interference isnt just recorder noise.
Anyone got data on whether the static correlates with any actual measurable readings at the time? I've started logging my EMF readings alongside the audio timestamps to try and cross reference it properly.