"Larry Dighera" wrote in message
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From the description of the noise, it would be consistent with some
sort of vibratory resonance. Having actually experienced it, can you
rule that out?

Probably. Resonance can happen in a variety of ways, and can sound and feel
like a wide range of things. But my experience has been that when resonance
happens, it amplifies an existing frequency, rather than introducing a new
one. I think resonance with something is unlikely in this case.

I did forget to mention that in addition to hearing the noise, I could feel
the "rumble" in my seat. It wasn't just a noise; there was a definite
(though equally subtle) vibratory component.

As another has suggested, the tach/MP gage should help in diagnosing
any loss of power associated with the noise.

Yup, hindsight is 20/20. Given the conflicting priorities (diagnose or
maintain control? ), I'm seeing a new reason for one of those fancy
engine monitors that I never thought of. They are always touted as being
useful for diagnosing hard-to-diagnose engine problems, but I never really
thought about the problem of watching engine gauges and dealing with
potential emergencies at the same time.

Pete