Why is my Win 7 PC uploading to a Win XP PC

[#1]

I have noticed via NetWorx that there is an intermittent upload from my Win 7 PC to my better half's Win XP PC - typical speed 2.4 kbps
This is a screen print from Kaspersky - any idea what would be causing it

[#2]

It's to do with SMB:
https://www.grc.com/port_445.htm

[#3]

Shows up on my Mac (networked with Win7 PC).
I can switch it out in prefs (Microsoft Domain Server) on the Mac when not needing to network. Leave as-is on the PC as such a palaver to alter it.
Thing that I don't fully understand (never have really got networking, tbh) is why, even when the network and sharing are switched off on the Mac sys prefs, there is still considerable sporadic traffic between the two machines showing up on the firewall logs (mostly on 139 tho). Don't know what the volume of that traffic tho.

[#4]

thank you - I now understand

[#5]

Didn't you know that "its good to talk" M$ took it to heart, loads of background chatter, from way back in the days of netbui.
Last time I worked on a real wan they tried to shutdown the WINS servers (on a remote site not telling us in the UK) that caused the whole "AD" network to take a flaky. I mentioned I had seen it in a NT4 network when the WINS servers were misbehaving, they then found out the Indians had shutdown the WINS servers (only ones on the wan), bringing them back up brought the network back up.
Don't know if they have finally got rid of it.

[#6]

the port numbers change but the process doesn't /