The rear pads have what's called "warning sensors" which is a small piece of metal that's designed to rub, giving you advanced warning before the pads themselves grind into the rotors, which gets more expensive.
Get new pads installed ASAP as they typically don't last long in S/V 40s as it is. A problem that those cars have is that the pad to caliper clearance is too tight so they rust easily, stick in place (don't slide freely) and wear out pre-maturely. When I replace those pads (and a few others that fit too tightly), I carefully grind the ends of the new pads a bit and lube them so that they move freely in the calipers as they should.