Sucking noise from engine bay.....vaccuum pump or not?.....

[shista240sx]

heyy guys i posted this on the general chat and should have posted it on this forum...anyhow i start up the 240sx and i hear a weird sucking noise coming from the engine bay. I at first thought it was the manifold but then said "duurrrrr!! its not" because it wouldnt start back up if it was...due to shrinkage of the gasket e.t.c. and i was told on here that it might be the vaccuum pump...i was trying to find one online but coulnt..so should i just go cold air intake or what?...I am probly going to buy the 240sx....he wants $2600 for it but thats a lot and i dont wanna give him that much....what do you guys think?? lemme know ! oh and the idle is rough maybe due to the vaccuum pump but i think its the sparks/wires/and cap so ill proly replace them if/when i get the car...