Yeah this has happened to me a couple of times actually. Once in an old farmhouse in Suffolk, the lights started doing this slow flicker - not like a bulb dying, more rhythmic almost - and then about two minutes later we all heard something moving in the room above us. Nothing was up there when we checked.
I always wondered if its an EMF thing, like whatever energy is present starts interfering with the electrics before it fully manifests. Read a bit about this in some demonology stuff too, where entities apparently draw on ambient energy and that can cause interference with electrical systems nearby.
Could also just be dodgy wiring in old buildings obviously, don't want to jump straight to the paranormal explanation. But the timing always seems too deliberate.
Anyone got photos or video of it happening? I've been trying to catch it on camera but never had my gear ready at the right moment.