I've had this loud buzzy-like idle for quite a while. There'* a few noises that seem to be different, but it'* hard to tell. I thought the SC coupler was bad, now I'm thinking the tensioner pulley? I checked the SC pulley for play, and I don't think there is any. It seems tight every which way. There'* only a slight 'tick' noise turning it left to right, that may be normal. I don't really know though as I've never had comparisons.
Also, though possibly unrelated, when I drive my transmission seems very whiney, but it'* always had some whine since I got it in April.
Anyway, here'* a video if it helps.
EDIT: Most would already know, but for those that aren't sure, this is not the HB.