Has the vehicle done this since the brakes were changed 3 months ago? If so, I'd return it to them and have them rectify the issue.
Vibration under braking usually indicates a warped brake disc/rotor. It may be that some other component is causing this such as a failing wheel bearing but it's most likely to be a warped rotor.
It's very possibly the power steering unit. When power steering units get low on fluid, the fluid gets old, or they start to wear out they can make whining or grinding noises. These noises can be low or high pitched, it depends on the model.
First you would want to locate the pump, then listen for noises from it. Get someone to turn the wheel until it's ...