I'd pull the wheels and investigate. Since you've swapped pads before, you know that the rear calipers are easy to swap/service. Take the pads out. Lube the sliding points on the pad backing plate w/some nice high-temp molybdenum lubricant. Also, lube the pins slightly and ensure they're installed correctly and tightened (sometimes I am in a rush and during a recheck I didn't tighten a pin properly, etc...so it happens).
The parking brake is internal to the hub, so should be no issues there w/regard to pad wear. Finally...post some photos so we can check out the issue. That always helps.