Gravitational waves buffeting the planet would provide a plausible source.
Gravitational waves are (in theory) created by rotating objects which are asymmetric. For example, a spinning planetoid with a large dimple (or bump) on its equator. Suppose a wandering planet (a.k.a. rogue planet) entered our solar system. If this planet was such a spinning, asymmetric object that passed close enough to our planet, then we would expect to be buffeted by its gravitational waves. If the planetoid was part of a rotating binary system of two planetoids of different size, then the same effect would result.
Events such as supernovae also create violent gravitational waves. A supernova event need not be nearby to create a big impact. Unfortunately, a supernova would create all sorts of additional effects which would make the gravitational waves the least of our worries.
A rotating binary system consisting of, for example, a black hole and a neutron star could produce detectable results at considerable distance, perhaps many light years.
Gravitational waves have the added bonus of compressing the atmosphere, which would cause the density of particles in the atmosphere to increase, resulting in much more colourful skies. When we look at a sunset, the colours we see in the sky result from looking across the tangent (to the earth's surface) to maximize the depth of atmosphere in view, causing the number of particles seen to increase. It is sunlight reflecting off these particles that create the colour of a sunset. So if the atmosphere was compressed uniformly, then we would see this effect in all directions.