Poseidon regulators would occasionally have similar issues, especially after half-arsed overhauls, often characterized as a "shuddering" in shallow water, frequently dismissed as just being the nature of pilot valve in Jetstream seconds -- a ready excuse for poor tuning; an easily-damaged valve (which I saw frequently); clumsy scratches to sealing surfaces; and even too high of an IP, more often than not.
Early XStreams had a funky whistling issue, if I recall, attributed by Poseidon to some weird "resonance frequency" issue between the ball bearing and actuating pin in the first stage, which seemed to have been solved in later models, after an industrial ruby, of all things, replaced the bearing . . .