In the early stages, rod knock can be very quiet, just a ticking, or you may not really hear it at all at idle. The classic rod knock sound is this: very little or no knocking/ticking as you accelerate, and then a loud knocking for a second or two after you let off the gas to shift.
I've had two cars die rod knock death, one was a Toyota that died very slowly (oil starvation at one point in its life), and took 2000 miles or so before it went altogether. The other was my 98 Cobra, which died a very sudden death from a spun rod bearing, took about 2 minutes for that one.
Dave