I'm not sure that that's normal. I'm not sure it's the ABS either, but it's certainly a possibility. My 2000 doesn't sound like a growling noise after startup. But I'm pretty sure they changed the ABS system a couple times through the years of the 3rd gen.

But I wanted to add that when you brake hard and ABS is actually set off, it makes a loud clicking/grinding sound and you can feel the brake pedal vibrate a bit. I've done that many times. The sound is very noticeable.

That's different from the very faint clicking/grinding noise heard soon after starting/moving it (at least on a 2000). I think every vehicle with ABS does some sort of system test when you start it and/or press the brakes for the first time. I think Toyota's ABS test is barely noticable. I have to really concentrate to hear it on mine.