love4dirt

so my girlfriend has a 94 civic ex. manuel transmission, 1.6 v-tec sohc. 12.5 to 1 pistons full exhaust aftermarket intake manifold and an intake. i cant remember exactly when this noise started happening, but almost everytime she shut her car off you could hear a high pitch squeal/whistle sound inside the car and when you got out you could hear it coming from under the hood. i figured it was just the pressures equalizing in the a/c and didnt feel like checking it, then i realized if you hit the brake petal it would stop. i am thinking it is indeed the brake booster i was just wondering if anyone has any other suggestions?