Kinda sounds faintly like letting the air out of an untied balloon, by stretching the opening.

This happens when pressing the brake pedal, but only when the engine is running.

I'm thinking the brake booster has a leak maybe.

Also want to note that this only happens if I press the pedal beyond a certain point. If I press even further, it also stops making the noise.

It doesn't seem to effect the braking, although the booster doesn't seem to assist much.

It takes more pedal effort to stop than my YJ does.

 

Is your brake fluid low at all?

 

possible vacuum leak in booster

 

No, brake fluid is not low at all.

I'm thinking booster leak too, but it's only in one area of the pedal stroke.


Also sometimes I hear a random clunk under the dash, that sounds like a hard plastic thing breaking. Totally random, too.