I'm hearing very loud clanks whenever the ABS engages under hard braking. I check the ABS enough (yes under safe conditions) and it sounds way louder and different than usual. It kind of sounds like some guy is banging on tin cans or dropped tin pots or something down there, which seemed to be driver's front, but I'm not sure. The clanks also seemed to roughly coincide with the ABS pulses or noises

I've already scheduled an appointment with the dealer, but is anyone familiar with what's going on? Could something be loose, and is this any kind of a critical safety issue?