When a passenger on A320 family, you always hear PTU running to assist when the gear is moving. The gear is a very heavy user* and causes a big demand on the engine pump.
After shut down you can sometimes hear the PTU ‘see-sawing’ in one direction then the other, as the Green and Yellow pressures bleed down.
* As a matter of interest; have you noticed how short the lever arm is that the retraction jack pushes on to raise the mains? The mechanical disadvantage of that must be insane. Imagine trying to swing the weight of the main gear up by pushing on that lever so close to the pivot. It must present a HUGE load to the retraction jack - hence why it is such a large diameter jack - and I am not surprised that the Green system needs some help with it !