Her1stcar

So the battery died in the 08 SEL I bought her for her 16th birthday. I put a new battery in and as soon as I hooked up the positive cable I started hearing a humming noise. I can't chase down the exact cause but it seems to be somewhere in the brake system because the vibration can be felt in the master cylinder and the brake pedal. Anybody else ran across this and can give me some pointers? Thanks