AW: Can you find it?

[Haible Juergen <Juergen.Haible@nbgm.siemens.de>]

Just a few ideas (haven't seen any schematics):

        >-- The telltale noise will correspond to a flickering on the
Feedback LED
        >(which I mistakenly referred to as the Input LED in my cover
note to
        >Oberheim -- mea culpa indeed).  When the LED for feedback
flickers at the
        >beginning or end of the note, or if it sustains below a
threshold loud 
        >enough to cause the LED to glow solidly, the noise rears its
head. 

Maybe the noise comes thru the supply voltages. My first guess 
would be this: There is an analog circuit (opamp most probably)
that is on the edge to instabillity / hf oscillation. When the LED 
flickers, this could mean (depending on the circuit), that the
supply current changes rather fast. This can be coupled to
the "sensitive" opamp over the supply voltage lines, and *could*
cause an effect like you described.

Things to try out: Bypass all opamps with 100nF ceramic caps
(from their supply pins to gnd), if they aren't already.
Bypass the the supply voltage near to the LED circuit with 100uF
elko.

May have no effect at all, but maybe it's worth trying it.

(This was based on the asumption that it's an analogue problem
- still there with mute on -  and the unit has a "cheap" power 
supply system. Which of course might be totally wrong.
If anybody has schematics and likes to send them to me, maybe
I can tell more.)

        JH.