Simply put, what you need is the effect of changing the tone of the sound irregularly.

Specifically, you can choose tone/tone bending/singularity in the effect. You can achieve the effect you said.

Actually, in AU2.0? And AU3.0? There are many plug-ins that can achieve this effect. But the general idea is to change the tone irregularly. Can also be adjusted according to needs. Using plug-ins directly is a relatively easy way.

(Pay attention to the screenshot)

I hope the above can help you.