You seem to be making the assumption that the whine is caused by AC from the alternator - which is correct in a way but all alternator outputs contain *some* level of AC. Most audio systems are capable of rejecting this AC - but your current audio/amp/wiring configuration is not.

It could be the AC level is too high or it could be the wiring configuration you have.

An oscilloscope is useful for viewing the waveform (shape) of the AC on the alt. output and can give clues as to the fault source but there are other way to diagnose the alternator diodes. You can measure the diodes with a multi-meter to verify they only conduct in one direction etc. but you need to open up the rectifier/regulator to do this.

The test you performed prior to your first question in this thread is the other simple test. Your result of 150mV of AC seems rather high - anecdotally, 50-100mV is normal but it can spike higher under load. Not knowing the charge state of your battery or the other factors affecting the electrical load on the alternator at the time, it's hard to say if 150mV is a problem.

How much AC is on the jumper terminals now that the filter is in place?

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)