[ICOM] Icom 756PRO Noise Blanker help

[KD7JYK DM09]

:I recently purchased a used Icom 756PRO which is a very nice radio, but it
: has something unusual about it.  When I turn on the NB, it makes a noise
: like a howling wind or kind of a screetching sound.  That is about the 
only
: way I can describe it.  It only does this on SSB, not on the other modes.
: I hear it with my headphones on,and also thru the speaker.  It is
: background noise dependent as it disappears if I turn off the preamp.

I do not have that radio, BUT, several others I have do that if some sort of 
digital signal processing is also turned on, the heavier the processing, the 
more the unusual noise.  Some radios will hold a setting, for example if DSP 
is turned on in one mode, it might not be in others.  Is the 756PRO capable 
of that?  Check the screen indicators carefully if no other ideas come to 
mind.

Kurt