Flanger effects with the feedback close to 1 ['doo.mp3'] can get truly nasty
but since I don't want to cause actual ear damage I just edited that file with audacity using the effect "compressor" and now it's just shattering, not life-threatening. _
Running the same effect on another piece here ['edd.wp3'] brought up a couple notes that had been too wimpy, makes that delicacy sound almost intentional.
These guys were done with a rudimentary set of pd gizmos, one inadequate (but touch sensitive) keyboard, csoundapi~ with fluidsynth opcodes and keyboard skills that 'Needs Improvement!'
but they do show that one can get some thoroughly nasty good sounds this way.
Having fun (listeners beware): https://www.dropbox.com/sh/7caeqrgt1inp7su/eWpPoCKtjO_