braking, all ok until I nearly depress all the way then it starts making a noise on 2004 Volkswagen Jetta

OK, I have called my mechanic but he hasn't called me back yet and am concerned...
When I depress the brake pedal everything is ok until I get to the "bottom" of the pedal, you know, keep pushing down, then poof, it starts making wonky noises. It is a low grumbly noise. Almost grinding but not quite. The noise is coming from the back of the car and almost sounds like the trunk.
To make do, I am downshifting and using the brakes as little as possible.
Any thoughts?
Thank you,
Amie

Asked by for the 2004 Volkswagen Jetta
1 answer
start to check all brake lines for leak and check master cylinder.