Grinding versus squealing
A high-pitched squeal is usually the wear indicator doing its job — a metal tab designed to warn you before the pad runs out. That is a warning. Grinding is what happens after the warning was missed: the backing plate is now scoring the rotor. The difference between the two is roughly the difference between a pad job and a pad and rotor job.
Why waiting costs more
A pad replacement caught at the squeal stage is the cheaper job. Once grinding starts, the rotor is being cut every time you brake, and rotors that are scored or below minimum thickness have to be replaced rather than resurfaced. Waiting turns the smaller job into the larger one.
Grinding only when turning, or only at low speed
A grinding or growling that changes with steering rather than braking may be a wheel bearing rather than brakes. A single grind on the first stop of a damp morning is usually surface rust flashing off the rotors and is completely normal.
What we would do
Road test, then wheels off to measure pad and rotor condition and check the calipers and slide pins — a seized caliper causes one pad to wear out dramatically faster and will do it again if not addressed. Photographs to you, price agreed, then the work.