peugeot 406 hdi 2000?

im a motorcycle mechanic and dont really work on cars much so a bit of good advice would be apprecicated
,lateley when i put my air con on it makes a knocking noise that can be heard from the blower vents in the car its not the fan as that makes no odds if i turn it down or even off ,its def the air con,can the pumps be serviced or is it replacement only ?i have changed the serpentine belt before so will do that again when i investigate the pump.also another probelm is that the fuel filter housing is making a pumping noise lateley too and it didnt used to do it i have changed the filter not to long ago just in case it was blocked up but it didnt fix it.