Must likely the noise comes from the ground path sharing. If the ground path from the radios audio is the same as that of the gyros the gyros ripple current will be induced into the radios. Check the ground connections of the gyros, radios and audio panel. Verify they are not tied to the same ground wire.Gyros ground path should not be shared with any of the COM/NAV or audio panel ground connections.Also check for ground wires loose or oxidized connections.

Orv

Regarding the installation of a noise filter. It should be installed as close to the power connection to the instrument as possible. A noise filter will reduce noise being carried on the power wire but will not eliminate noise that is radiated from the instrument.

jplaxton00 Wrote:
-------------------------------------------------------
> Hi All;
>
> Since my first post, I did some more testing and
> determined that the radio noise is definitely
> coming from the TC, but not over the wiring.
> Using my handheld radio, I turned the master
> switch on and picked up the same noise.  The pitch
> changed as the gyro spooled up, and when I shut
> off the master switch the noise stopped.  I called
> Mid-Continent, the manufacturer of the unit and
> they are sending me an exchange unit to try.  This
> is the new "B" model which uses an AC motor and
> internal line filter to suppress noise.  I'll post
> the results after I install the unit.
>
> Jon

Keep in mind that the antenna on the handheld is next to the gyro while the antenna on the radios is outside the cabin environment. A well shielded radio will not pickup noise from the panel environment. Hope the new unit fix the problem.

Orv