I have had a consistently inconsistent problem whe3n listening to my
AM tuner in my 90 GL.  The head unit is a Sony XR-C6100 but
I'm  pretty sure it's not the Sony's fault.  BTW, it has two Rockford
Fosgate amps driving the stereo speakers, so the Sony chip amp
doesn't get heard very often.  The radio makes the same noise whether
the R/F's are thumping or not.

Symptoms are as follows:  I will turn on the unit on and be listening
to either a local or far away station and after a few minutes, there
is a very annoying sound that resembles someone taking a signal
generator and running from about 100hertz to about 2k hertz.  it
oscillates some and is intermittent.  The reason I don't initally
bame the Sony is that when I take my hand out of the driver's side
window and touch/ wiggle/massage the antenna shaft, it changes pitch
or briefly goes away.  Other than bad grounding, what could be
causing this strange nosie.  If it were bad ground, wouldn't it also
affect FM performance too?  The FM side is fine.  FWIW, the antenna
is the model that has the really skinny black solid shaft and it
threads into othe unit attached to the body.  Any help would be
greatly appreciated.

DM&FS