the fluid on the ground is most likely water, from underwing frost melting after the aircraft has been refuelled. -talking from experience.
airbiii make alot of strange noises on the ramp, dont ask me what they are tho, i can only assume hydraulic pumps and a/c packs.but as for the PTU ,totally normal yet unnerving sound! have also heard ptu operate on ground with both engines shut off.(thought it was unusual)
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