Does anyone know if the factory front brake pads begin to chirp (give an audible signal) just before they are in danger of going metal-to-metal on the rotors? Ours are getting thin and I don't want to chance it if the pads aren't designed to chirp....

It's a 2005 S-Type 3.0 with 30,600 miles....

 

In all reality I don't remember if there are wear warning tabs on the pads. The thing is that the wear warning tabs are like the tread wear indicators on tires. The part should be replaced before they hit that mark. Those indicators are designed to avoid liability when an operator neglects to check to see if a part is worn out. If the pads seem thin, they probably are and should be replaced.