I'm closing in on 10k miles on mine and I haven't really noticed a difference in the idle. It might be a little louder, but it's still really quiet. I'm not outside of it while its running much and I can't tell any difference from the inside.
I'm with Johnmo, maybe a hair louder, but not really noticeable unless I'm parked near something that the sound can reflect the sound. I can't really hear it when I stop if the air is running or the radio is going.