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what he saidI'm not familiar with that style of reg (servo ?) but it's not uncommon for a second stage diaphragm to "vibrate" out of water dry. I have a few that do and a few that don't. It in itself is not indicative of a problem. Breathing off a reg on land is not the best way to assess its performance. I'd take it for an actual dive first, I suspect you may be pleasantly suprised.
the inhale and exhale diaphragm are unusual in that design and both on the end of the reg. Vibration on both inhale and exhale out of the wa wa would not worry me much.Is the vibration on inhale or exhale?
Exhale is fairly common as the exhaust valve does not has any water on its back side to dampen that movement. Inhale is unusual but it may be something about that servo valve. If the problem is on inhale, I would talk to the shop.