[R-390] R-390A 800 cps tone in cal below 8mh bfo off

[Larry H]

Hi all,  I'm working on an r390a and just noticed that when I'm using the calibrate signal below 8 mh, I hear about an 800 cycle tone with the bfo OFF. It is weak, but it's not right.  This rx now works correctly in every respect xecept for this one little thing.  The cal does work normally above 8 mh.  The antenna is disconnected, so no feed through there (ant is disconnected in cal anyhow).
I've not dug into this yet and was hoping someone might have seen and fixed this before.  I searched the forum and net, but no hits.  Any help or suggestions would be greatly appreciated.
Regards, Larry