Two questions please? suction in tank, hydraulic pump rattle

[falling-out-with-my-car]

the car Citroen xantia 1998 Mk2 S reg 1.9TD estate.

Ever since Citroen had my car in for emergency surgery to replace all of the serpentine belt pulleys about three years ago I have had this deep dronning noise comming from the engine at idle.
I thought maybe it was the compressor on the air con circuit and symptoms have been know in low air-con lubricant to cause this noise.

after some time trying to track the noise I have actually now found it but dont really understand the mechanics oif the componants enought to fix it.

On the back of the Hydraulic pump is a shock absorber (coiled spring) when the engine is idling the vibration is comming from this shock absorber if I put my hand on the shock absorber the dronning noise stops. it looks like there is a bolt at the bottom end of the shock absorber but wether or not it should have a nut on it I dont know there is no nut on mine just a bear thread. citroen put this new shock absorber in. in fact it is something I had never noticed until the car had been to citroen.

the bolt that holds the lower end of the shock absorber looks as though it enters somewhere near the serpentine belt end of the engine.
has anyone else had this vibration? & how did you fix it?

finally and I hope this is the simple one every time I remove my fuel cap I hear air rushing in to my diesel fuel tank, I am guessing that maybe the breather hose is blocked but I am not sure which hose in the rear wheel arch is the breather line can somebody clear this up for me please?

thanks in advance regards Nigel.