[s-cars] Ground loop problem in aftermarket stereo install question.

[Tim Sexton]

  Hello All,
    I have just installed an aftermarket stereo system in my 94 S4, and
have what I think is a ground loop.  However, being new the the car
stereo world, I am going to run it past some of you experts out there.
 The system consists of:  1.  Blaupunkt Munchen head unit  2.  Kenwood
KAC Q74 4 channel amp  3.  Blaupunkt CDC A08 changer  4.  Blaupunkt 5.25
components, front doors  5.  Pioneer TSA6999 6x9 rear fills.
    What occurs is,  with the engine off,  I can hear loud static and
electric motor noise when the head unit is in CD mode.  When I change
tracks on the CD, it sounds like you can hear the arm moving.  Also,
there is less static, but still audible, when the head unit is in tuner
or changer mode.
    For the amp, I pulled 12v directly from the battery, and pulled it's
ground from a tail light ground.  For the head unit, I pulled 12v from a
wire in the previous harness, and pulled ground from a ground point
under the dash.
    Does this sound like symptoms of a ground loop?  How does one
correct a gound loop?  What exactly causes a ground loop?
In addition,  I had the exact same problem when I used the Munchen to
power the factory Bose junk via the pre-amp outs.
Thanks for any advice you can share.
Tim Sexton

94 S4
87 5kcstq
86 4kcsq