radio noise

[David.Payne at brinksinc.com]

I've got intermittent ignition noise in the rear speakers (only) in my '89
90q.  If I pull the fuses on the speakers it goes away, if I adjust the
fade full front it doesn't go away.  The noise is sometimes triggered by
going over bumps in the road.  This car had a CD changer installed and
removed by the previous owner who cut both antenna leads for the FM
modulator.  I've spliced both leads back together, but the shielding is
obviously not as good as original.  This car has new plugs and wires from
Blau.
Thanks for your input.
Dave.