On Mon, 6 Sep 2004 21:44:37 +0930, "BruceM"
wrote:
I would think that it is just simply a resonance factor.
Ever heard one of those old Cummins 160's?
Let them idle & they are as quiet & smooth as a church mouse. Increase the
revs very slowly & you'll find that at 1400, 1600, 1800 & 2000 revs they
just about shake out of the chasis. (truck)

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The vibration in this case is way beyond anything normal, and the
generator is designed to run at a steady 1800 RPM regardless of load.