Thanks for the feedback on typical ABS sounds. The sound I hear is not a groaning or vibrational sound; it's more like the sound an engine would make when cooling off after being hot, except louder, and more percussive. Like a "tacka-tacka-tacka-tacka" kind of sound. I haven't really inspected the brakes themselves yet, so I'll take a closer look at the caliper/rotor/pad assemblies and see if there is a problem there.

Thanks again!