Weird Resonance at 2800 RPM after oil change

[Colonel Nikolai]

I've changed the oil and I notice a strange "middle C pitched" harmonic resonance at exactly 2800 RPM. It may have been there before but it's louder now, coming from the center of the engine. The bike seems to run just dandy, its just really strange sounding.

I was using Amsoil. I changed to a synthetic Rotella Racing 4t, bright red stuff.

[classvtony]

My 955i does a vibration at 2800 to 2900 or so feels like a metallic hum. Low so not sure what pitch it is.