I had a buzzing noise exactly like yourz. I thought it was something in my trannys or clutch at first. Later I thought it was my cat's heat shield rattling. It turns out that it was a bolt missing from one of the exhaust piping that goes to your transmission casing (I think it was the transmission casing). But my buzzing noise came on exactly at 2000rpm. I'd check all the bolts to make sure every one of them are bolted on still. They tend to fall off time to time.

Tuner