What I would do first is a filter calibration. It's possible this will
fix your problem if you are lucky.

Mark-

I have the older IC-706, and your instructions worked perfectly on it as well.
However, I couldn't tell any difference in the sound between USB and LSB after
the calibration was complete.

The difference in sound isn't extreme, just enough to be annoying. Further, it
is about the same with both the normal filter and the narrow SSB filter. I
tried the calibration with both filters, although the "NAR" indication goes off
while the process is being completed. I also tried it with the IF shift at
both extremes, with no noticeable difference in the results.

Any other ideas?

73, Fred, K4DII