Barry,
One possibility with the vibrating hose is it could be resonating. Everything that can flex will have some natural frequency and normal water flow through a flexible hose can start and maintain oscillation. If there is no air coming out of the return I would guess this to be the case. A resonance would cause it to vibrate at one frequency and the vibration would be regular and not erratic. If it isn't vibrating enough to cause a problem like eventual fatigue of a joint then I'd just live with it. Shortening the hose may help. Best I can do for now.
Al