Help! With Annoying Problem

[Bobnic]

hi i own a Toyota Altezza RS200 Z ED i'm having a problem with an annoying sound coming from the car, it a a strange watery type noise i hear when i turn on the engine and it gets louder sometimes when i rev the car. the sound sounds like it's coming from the front somewhere in the dash or engine bay. i took it to a mechanic to have a look and he said its the water pipes for the air conditioning making the sound. but when i first got the car that sound was not there i was wondering if anyone would know what that sound means and if there is a problem. or can anyone give me some advice how to get rid of that annoying sound