Buly,

You mentioned picking up noise from many sources.  Bob Nuckolls provides
several hundred pages of advice on this site:

http://www.aeroelectric.com/FAQ/AeroElectric-List/AeroElectric-List_FAQ.pdf

Type "noise" in the Acrobat 'Find' feature (binocular icon).  Quite a few
sources of noise, including motors.

Regards,
Chris Sargent

Here is a problem for you large brained engineers: My radio is picking up
noise from all the electrical motors including the alternator. I took the
alternator to the shop and checked "as new". When I disconnect the coax from
the radio, the noises stop, which leads me to believe the antenna coax is
picking up the interference somehow. Guy at the airport suggested a clamp-on
ferrite filter on the coax. I bought one tonight, but did not have time to
test it.  The offenders are: fuel pumps, nose gear motor and alternator.
Any Ideas?  Buly