akry,

Is your cd changer connected to the head unit with a fibre optic cable?
If it is I think that the only head unit that will be compatible with your cd changer (which will still need an adapter) is the Alpine one. All the others I know of don't use this type of data transfert. (Sony did two units with such Fiber optic inputs).
Benzmac refers to an amp, I didn't know that there was an amp in the W140 class Check the ground connection in that case, usually when the amp's ground is connected to the body of the car or is not connected to a pure ground (like direct connection to the battery or the radio's electrical system), these electrical interferences come from there, check it out.
Hope this helps

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