Possibly the hiss comes from the signal not being lined up properly with the SSB filter.
If the frequency is low in relation to the filter it will pass higher frequency noise.?
Some radios have if offset and you can hear this in real time.
A check of the LOs etc might help determine if this is the case.?
It has been a while since I have looked at the IC-7000 block diagram or schematic, but it could be an answer.?
Does this happen in AM FM CW in addition to SSB?
