Another alternative to eliminating the 2010's muffled audio in narrow mode is
to replace that stock MuRata 55JT 455khz filter with a MuRata 55G 445khz
filter. That's right, it's the same filter Sony used in the wide position.
There is enough circuit inductance in narrow mode to reduce bandwidth & hasten
hetrodyne whistles; whilst the 55G makes voice more intelligible, especially in
sideband mode. This mod was one of Bob Grove's "Tips of the Month" in his
October 1999 Monitoring Times column.