Well, I assumed they're bad when I measure the contacts with a meter and they don't change when the green line has 5V or is open. To me that's a 100% test of functionality, and two of them were bad! I actually don't hear a noticeable buzz from my DZ-1008's, but I do hear the click when the actuate, if they actuate!
I had actually installed the bad relay with the "assumption" that I wouldn't get a second bad one, that will teach me to assume!