Ground loop problem in aftermarket stereo install, 94 S4

[Tim Sexton]

Hello All,
    Many thanks to everyone who replied.  I have discovered, through the
process of elimination, that the audible noise when the head unit is in
cd mode is because of a problem with the head unit itself.  When I
isolate my amp, there is no noise whatsoever.  But, regardless of where
I power or ground the head, or where I run my interconnects, the noise
that can be heard when playing a cd is unchanged.  Thankfully, I can
still use the changer and tuner, until I can get Blaupunkt to fix it.
    Anyway, thanks again to all.  I certainly learned a great deal about
grounding car stereo components from this!  Now if I can just get the 49
pieces of  my interior back together I'll be in business :)

Tim Sexton

94 S4
87 5kcstq
86 4kcsq