Seems like it is worst at Midnight. Of course, the fluff-brains would call that traditional and want you to believe it had to do with astrology, the position of the stars, the moon's orbit, or what-have-you. I think it's crap. I just think that is the time when the world's grip on reality is at its weakest. I think that's all it is and nothing more.
The world is what most people believe it is. When everyone is awake and thinking, nothing supernatural or disturbing happens. When everyone is asleep, dreaming, using that monkey-brain at the back of the one we use all day, the one that just reacts, fears, scrambles up its tree to howl, that's when the stuff that we can't believe during the day comes out. We believe a lot of things deep down in the dark that we don't believe in the light of day.
So when I hear grumbles from the grave I don't doubt my senses. I don't panic either. I just walk on by and let the restless ones do what they have to do and I try to cope with the problems that affect me during the day. I right the occasional tombstone. I re-seed the grass that mysteriously dies. I report the "vandalism". Occasionally, I shout at kids that stumble onto one of the really active graves, but unless they do so I just let them sit down in the back corner where they think I don't see them and let them spook themselves.
I just work here. It's not up to me to fix the world.