[rescue] What is this traffic?

[microcode at zoho.com]

My network is an ADSL router into an 8 port TP-Link unmanaged switch. For a
long time now, when my network is idle (as far as I know) the switch has
been showing a very high level activity on the line from the router while
the router itself shows no activity on the WAN/LAN. This is 100% of the
time, even when no devices other than the router and switch are powered on.

I have no evidence of anything getting to any of the boxes on my LAN. iptraf
and netwatch, logs, etc. show only the expected activity (none at idle and
normal poor performance when using the net). Activity on the LAN just lights
the switch indicators and doesn't go outside as far as I know.

I have hard-reset the router several times but have not found a way to reset
the switch. I powered it off for long periods but as soon as I hook it back
to the router the activity goes sky high again.

Is there any way to see what the traffic between the router and the switch
is without extra equipment? Does anybody have any idea what this could be?