Ray Andraka wrote:

We flew it with the alternator field turned off, no change, which I
think rules out the charging system. I'll get him to do an in-flight
mag check when he gets it out of annual to see if it goes away on one
set or the other, good idea.

The noise is an impulse noise, could be ignition noise except it doesn't
seem to change at all with RPM. It does seem to be related to vibration
however, so I suppose a marginal ignition lead could do it. It comes
across as bursts of static. Not sure really how to describe it.
\

Simple things first. It seems to me that you have a vibration induced
bad connection somewhere. With engine off, master and avionics on, while
listening to the headphones:

Bash the panel alongside the COMs with a plastic screwdriver handle.

Thump the audio panel.

Thump the panel near where the mic/headphone jacks are mounted.

Reach up under the panel and flex the wiring bundles.

Twang the antennas.




Some likely non-vibration induced sources that you may not have thought of:

Disconnect the plug(s) at the rear of the turn coordinator or electric
gyro, or if you have pullable breakers, turn them off.

Do you have a motorized beacon? Turn it off.

Turn off the transponder.