Small overnight usage recorded, even when PC is swiched off

Plusnet BB has been installed in our church office for just over 2 weeks. Browsing the usage figures I notice that every off-peak period - midnight to 8am - shows some activity. It's very small, typically 50 to 150KB, though on a couple of occasions it's been around 1MB. The total over 18 days has been about 4.2MB.

In the grand scheme of things it's insignificant but I'm curious as to what may be causing the activity.

The router is left switched on, but the PC is off. Clearly it's possible that someone outside the church is using it for their own purposes but as the usage is so small I'd wonder why they bother.

I'm wondering if the router itself creates some traffic, if so what for and would it be enough to account for this?

Router performing checks for firmware upgrades/NTP checks plus the random noise of the TCP/UDP packets from the Internet

Thanks, that'll be enough to explain it I think.

From PN View your Broadband Usage FAQ:

3. Why is usage shown at times when I'm not using broadband?
Your router will respond to network traffic even if your computers are switched off. This causes tiny amounts of usage (classed as background traffic, rarely more than a few KB or MB) to be recorded. This is perfectly normal and nothing to worry about. We recommend leaving your router on at all times so you can get the best broadband speed

Thanks! I'd looked for something along those lines but failed to spot that