About the time I first had to re-adjust chain tension on my brand new drivetrain, that's when I noticed how quiet everything had become. At first, it was a constant tiny coffee grinder sound, not really loud, but loud enough to be slightly annoying. I would slather the chain with lube, which helped a bit, but it was still there. Now it's virtually silent, impossible to hear over the hum of the tires on the road and the wind in my ears.