You must be using hi fi phones rather than communications, limited band, 300
to 3000 Hz phones. If you use high impedance phones, or Comm phones, you will
not hear this noise which is the microprocessor noise. It is only detectable
on mine if I use very HI FI phones. An audio filter helps, but the better way
is to listen to HF with communications phones so your brain and ears will not
tire from extraneous noise. You might try better power supply bypassing on
the audio stage if it is established that it leaks into the audio via that
bus. I did not go to the trouble, when I found mine worked so well with
Military phones.
I use 15000 ohm impedance HS 32/U military headphones from Surplus store, and
have no whine in my Scout, nor do I have to do more than barely crack the
volume control. Any old Trimm 2000 ohm ham headphones should work almost as
well, or you could use any phones with the W3NQN audio filters, if you match
impedances.
You can hear the same microprocessor noise if you listen to many of the
Yaecomwood imports with hi fi phones.
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