Hi,
Interesting, I have had lots of problems with ceramic caps and distortion in audio circuits.. Note Y5V dielectric is about the worst and X7R isn't much better, anything above 0.1uF should be regarded with suspicion in a ceramic. Unfortunately ceramics are quite microphonic too, and this...
You didn't mention what type of inductor you are using, from the symptoms described it sounds like you are using an iron-cored or ferrite inductor, and that the core is saturating.. I would recommend you use a large air core inductor and if you are handling significant power a speaker cross-over...
