[Elecraft] K3 settings question

[Chris]

Hello,

I am a happy owner of K3.  I came across another K3 with an early serial
number below 1000 in good condition at a local hamfest.  It works well,
somehow better than my current K3, so my first reaction was, Wow.  It seems
to have a lower noise floor and sounds slightly better.

My question is, how can it be?  I have yet to compare all the settings for
either radio.  The filter in my current K3 is 2.7kHz, and the new (new to
me) K3 has 2.8kHz.  I am not 100% sure these filters can make that much
difference.  Besides that, all hardware configurations are pretty much the
same.  They both have updated KSYN3A modules.  This K3 with a lower serial
number has KAT3, and my current K3 doesn't because I have KAT500.

Any suggestions?

Many thanks,

Chris KM1B