Phantom usage

[#1]

To sort out my problem with the SNR jumping to 15dB I have now fitted a Netgear DG834GT Router. Having tweeked the SNR I understand that I need to keep it switched on, something I did not previously do.
Since then I have noticed my usage has increased. Yesterday afternoon I set a WEP password and checked that I could communicate with my PC wirelessly if I needed too. As I also have a wired connection I then switched the Router Wireless off, checked it was off, then turned off the PC wireless card. I then switched off the computer.
Today I note that PN are reporting that I used 228kB of free usage last night. Is this normal, that is, does the router chat away on its own in the night? Does this also happen in the day and eat up the free allowance?

[#2]

This is absolutely normal. It's coming down the wire from Plusnet and consists of things like port scans etc.
Unless you have an attacker, leaving wireless on (even WEP only) will not cause any increased traffic.

[#3]

There's also KeepAlive messages between the router and the ISP, NTP packets to synchronise your PC's & or Router's clock.  Tiny little packets sure, but ultimately every little counts . . .
If I remember I'll keep an eye on my router stats between going to bed and the morning after to see what I have consumed.

[#4]

Shouldn't have any ports scans if you've got the PN Firewall on! About 86K was my last overnight with no usage.

[#5]

You will, with the default PN firewall settings, since only some ports (the more commonly used service ports) are blocked.  Typical port scans cover selected service ports, or all ports below 1024.  More involved, random, or persistent port scans can probe any port all the way up to port 65535.
From 11:30 last night to 09:00 this morning I had:

Inbound: 378,581 bytes
Outbound: 254,306 bytes

going through my router.  All PCs were switched off.

[#6]

Thanks for the responses. My PN firewall is set to the default 'Low'. I have run Shields Up, which says that all is well. I accept that 250kB a night will not break the bank so now I understand what is going on I will stop worrying about it.