One of my portables which I like has a problem with noise. The odd thing is
that when using the mains input the noise appears only on the lower SW and
all MW frequencies. The lower I go the more it becomes a whistle. This
occurs whether I use the supplied AC adapter or a DC-DC converter. For the
veterans, does this imply that the input jack itself is somehow generating
lower frequency noise? Has anyone else ever experienced this sort of
thing? I would consider a ferrite bead on the cord at the adapter but
since it seems to be related more to the jack than the adapter, would a
bead on the adapter cord right next to the jack input make any sense? Any
other suggestions?

Thanks very much.
-Al
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