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Had a weird issue with prop control on descent. Shortly after beginning my descent into KMLB, I lost power, followed by an extremely loud buzzing coming from the engine. Tach showed immediate rise to 2550, so I followed the prop overspeed checklist. Nursing the throttle, I found a sweet spot where I could barely hold altitude at around 100 kts. I was close enough to KMLB that I was able to declare emergency and safely land directly onto the runway. This buzz was loud enough that it was difficult to understand the tower over an ANR headset. Upon landing, checked airplane over, no oil anywhere on the bird, or dripping onto the ground, no grease on the propeller blades, and no loss of oil as I checked the oil quantity the next day. In fact the oil was freshly changed, and it still had the sweet honey color of fresh oil. I pulled the engine monitor data, and correlated it to the flight path. Here is what the engine monitor data showed. Oil Pressure- nominal, no change through the entire flight. Close look at the tach data showed variation in tack readings from 2480 to 2510 regularly over this leg. I don't really see any standouts when I review the engine data. When the incident occurred, there was a significant spike in revolutions to over 2550 rpms, but then returned to 2410. Going to the mechanic tomorrow. Suspect a leaking propeller piston, or flat spot in governor? Thoughts welcome. Especially the source of the loud buzz!!