A ginding noise from the left front, not the brakes
If you've pulled the wheel and visually inspected the brake pads and rotor and there doesn't appear to be any contact between the backing plate and the rotor then a wheel bearing is all that is left. Take a look at the inside of the wheel too. Sometimes people install aftermarket wheels with the incorrect offset that work fine until the brakes wear down some and the caliper contacts the inside of the wheel.
One easy way to check if the wheel bearing is out, jack up the front of the vehicle on the side you're hearing it from, then wiggle the tire back and forth. Both on the sides, and on the top and bottom. If it is the wheel bearing there should be four bolts, 5/8 I believe or 9/16. Use a breaker bar to get them lose, and then go to your nearest mechanic store, get one and then the tightening sequence is the corners. so top left, bottom right, bottom left, top right.
Shocks or Body springs have gone out , maybe you axle bracing or the bushing is faulty...
Looking for a Used Mustang in your area?
CarGurus has 45,735 nationwide Mustang listings starting at $1,999.
Search Ford Mustang Questions
Ford Mustang Experts