'03 Impala: High-pitched humming w/brake issue

It started with my "Low Brake Fluid" light coming on and a high-pitched humming noise coming from under the hood (sounded like a fan). Filled the car with brake fluid and had the lines checked for leaks - brakes are working fine & no apparent leaks. But the humming is still there, only when the car is in motion - it stops when idle/park and gets louder/"faster" with increased speed. Any ideas? My mechanic doesn't seem to have time or even desire. Thanks.

It started with my "Low Brake Fluid" light coming on and a high-pitched humming noise coming from under the hood (sounded like a fan). Filled the car with brake fluid and had the lines checked for leaks - brakes are working fine & no apparent leaks. But the humming is still there, only when the car is in motion - it stops when idle/park and gets louder/"faster" with increased speed. Any ideas? My mechanic doesn't seem to have time or even desire. Thanks.

Sounds like a wear sensor to me.
Brake pads have a metal tab that rubs the brake rotor to let you know it has worn to the point of replacement.
The low fluid would indicate they have worn down somewhat.
Better find a new mechanic before the grinding starts.