Alternator noise on Xmit only

(I have only "seen" this plane on the telephone, but the folks I am trying
to 
help were pretty clear about the symptoms)

The basic problem is alternator noise on the transmitted carrier, receive
is OK, 
and alternator noise is not apparent anywhere else in the plane.  The
pitch of 
the noise changes with engine RPM and disappears when you switch off the 
alternator.

-No complaint of alternator noise in the intercom.

-The symptom is the same on both radios.

-If you turn off the intercom and key the radio, it still transmits the 
alternator noise.

-They have tried different headsets

So far, I have told them to carefully check any ground straps under the
cowl and 
to check that the radio stack has a good ground.

Any other advice?

(Jim's take will be especially appreciated)


Thanks
Vaughn


-- 
Will poofread for food.