I found where the buzzing sound is coming from. It's actually the overvoltage relay. I didn't know that a relay can be buzzing and vibrating. Just ordered the relay and one year maintenance supply from the FastLane. I will keep you guys informed as soon as I replace it.
BTW, my order number is 016. Are there just 15 people ordered parts before me? Anyway, I think the price is very good, and the OE parts should be first grade based on my past experience with PartShop.
Harry (94 C280)