random clatter from engine, air in fuel line? :s

[andymccabe13]

I have a p reg 1.9 td and have noticed noisy clatter from time to time. When running normal (70% of the time) its really quite and runs brill, but occassionaly it clatters usually when going through gears (as the revs drop) or idle. I have noticed theres usually air in the bleed buld and usually takes 2-3 pumps to go hard. any ideas?