Non-isolated USB sourced noise on various synths - definitely seems to be a thing

Probably not on the cheap ones.

Anyway I did a quick test, I connected Seqtrak and KO2 to a power bank, audio from Seqtrak into KO2, first you hear with the isolator, then without, so it definitely gets rid of the noise in this case.

Edit - the white noise is just iPad mic picking up from speaker.