Hi, I designed  an electronic crossover for my  car stereo a while back. I too
used a charge pump to produce the (-)V for the OPAmps. I had a huge problem
with the switching noise. I tried low ESR caps of various sizes. Even after
boosting the switching FREQ above audible, it was still there. Don't no why.
Finally I added shielding (aluminum foil) around the charge pump IC and
components and it eliminated the problem completely. I'm not sure you have the
same problem though. It may be worth experimenting. Good luck. Matt.