I don't get it, you said the last time you took your car in they said you needed new brake pads but the shop you took it to recently said nothing is wrong with your brakes?
:shrug:

I'd say replace your pads and the noise should go away. I'm on my third set of pads on my car and both times right before I replaced my pads, they made the same noises you described. It was weird at first because I thought worn out pads only made noises when you pushed down on the brake pedal but mine always made noises when driving, got progressively louder as I drove faster and would disappear altogether when I pushed the pedal down hard.