[Elecraft] K3 Sensitivity problem on 75/80 and 160 meters

[Jan]

I have a K3 that works fine on all bands except 75/80 and 160.   I have 
a backup rig, an IC-730 from the 1980's, that has 75/80 but not 160.  I 
did an A/B with the two rigs on 80 meters, and both the S-meter and my 
ears tell me that signals are 5-7 S-units weaker on the the K3.  S/N is 
clearly worse on the K3 than on the 730.

Can someone clue me as to how to chase this down?  Even if I have to 
send a board back to Elecraft, I would like to do that rather than send 
the radio.

Thank you,

Jan, KX2A