Yeah this happens to me too. Not done loads of recordings but the few times ive caught anything interesting theres almost always a burst of static or like a frequency shift just before it. Wondered if it was interference from my equipment but it happens consistently enough that i dont think its that anymore.
Someone told me once it could be the spirit drawing energy from the air around the device, which would make sense if you think about how cold spots work. No idea if thats scientifically sound but it fits with what ive experienced.
Curious whether anyone's noticed a pattern with how long the static lasts before something comes through, like is it always just a second or two or sometimes longer? Mine seems to be pretty short, maybe 1-3 seconds max.