Create wierdly cyclic motion in your sound with Flanger.
It's sort of similar to a sweeping comb filter.
Flanger Creates a flanging effect by mixing the audio with a slightly delayed version of itself. The length of the delay can be adjusted manually and modulated. Optionally, this effect can also add a phase shift between the dry and wet signals to create an infinite barberpole-style flanging effect upwards or downwards.