At around 1900 RPM I pick up a bit of vibration (or rather a hammering) that I can feel right through the throttle. I'm hesistant to call it a vibration because the frequency is a little too low. Doesn't feel like transmission or drivetrain; definitely feels like engine. Acceleration is smooth through this zone, but once I get over 2000 RPM it smooths out again. Don't know if this is normal. I've only noticed this in 6th; I'll try other gears. Anyone else experiencing this?