Why (in universe) does the use of a cloaking device cause a 'wobbling' effect of light?

Whenever a ship uses cloaking technology (well, at least in terms of the Romulans and Klingons in TNG), there is a 'wobbling' effect of light as they activate/deactivate the cloak. Now, I know that cloaking works by the bending of light and that this effect is used to make it apparent that cloaking is occurring, but my question is why does this 'wobbling' effect of light occur (note I'm looking for an in-universe explanation of this, not necessarily a scientifically accurate one, but more of someone in universe (or even an authority e.g. a writer out of universe) explaining the reason for this)