Air Conditioning - Please Help!!

im currently in an apartment on the 3rd floor, the wall where the a/c comes into the building is making loud noises. the noises it makes sounds like pressured water running up the wall, when you put your ear to the wall it sounds like running water. it starts out soft and then randomly gets very loud, like louder than the tv, im not joking i hear it in the other room. what is it?? please help me and give me some direction. like all apartment complexes they say its normal, im not an a/c expert, but i know its not, its never made noises like this before. any help would be appreciated. thanks so much.

Do you have your own A/C or is part of a larger system? It could be part of a chilled water system which serves the whole complex. Often you can hear water flowing thru the pipes with a chilled water system. You shouldn't but often can. Could also be the sound of refrigerant in the piping but you should not hear that except for less than a minute when the system first comes on.