Q: E30 stereo hum?

[tom.murphy@xxxxxxxxxx]

Hello BMW Experts!       I just installed an MTX amp in my '87 325is, and
need
to ask a few questions!
1) How does the negative speaker signal get back to the head unit?  The
only ground I
    can find behind the radio is to the chassis.  Does the amp ground this
signal to the
    body also, and that is how it gets back to the amp?
2) In back of the head unit, there are two cut white wires, one each from
the little rubber
    'plugs' which also originate the R & L speaker hot wires.  Are these
two cut wires (now
    connected to nothing) actually speaker negative wires?
3) After checking out the condition of the stock wiring, I put in all new.
The amp is hot-
    wired to the battery, with the wire going around the tail of the
trunk(battery in trunk),
    thus contacting no other wires.  The amp is grounded to the body, with
about a foot
    of wire.  The stock hot and ground wires are only cut in the back, thus
have current
    running through them.  Could this be causing my hum, since they run
next to some
    of the speaker wire?  If so, where can I disconnect this hot wire?
4)  I put in new speaker wires from the head unit to the amp, but am using
the stock
     ground wire, since I couldn't figure out where that wire was going.
How have you all
     done this ground wire?
5)  The offending hum is related to engine rpm, but is not a rat-tat-tat of
the sparks, but a
      nice whining hum.
6)  Who made this head unit, and is it a bad Alpine, or a mediocre Pioneer?
This one
     has weather band, sliding bass and treble, and the front-rear fader in
the dash (which
     I have taken out).
          With all the recent talk here about upgrading E28 and E30
systems, I think
this may someday work (with digest help, of course).
                    TIA!!          Murf  '87 325is      BMWCCA 79550

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