Yeah there's a noise thing above 15 kHz that you can see in Audacity spectrum view or hear if you slow the playback.
is there shit at 18khz? i didn't even hear it on my headphones. I'll have a look. I've noticed pads with chorus sometimes cause it, very weird.
a short pad sample, pitched and layered on top of itself, then passed through a pulv for envelopes and lfo