Recent simulations of perturbed of AdS black holes have revealed nonlinear, turbulent behavior in purely gravitational systems. This encourages a search for turbulence in other gravitational systems, especially realistic black holes. I will report on a new method for computing the quasinormal mode frequencies around black holes slightly deformed from Kerr, which allows for a first accounting of nonlinear mode-mode coupling. We find that scalar fields around perturbed, rapidly rotating black holes suffer from a parametric instability, analogous to the onset of turbulence in fluids. I will discuss other applications of our method, specifically to the quasinormal modes of weakly charged, rotating black holes, and future directions for this work.