Hi Rob,
I also get a some strange unrelated traffic: ping replies, SYN-ACK on various ports, pings and SYN targeted to random IPs on my subnets. So nothing new here. I studied the source addresses for some time: china, russia, and alot of "this IP range is really wold wide" according to RIPE. Since they achieve nothing, I choose to ignore them, along with some tight stateful firewall rules.
Marius, YO2LOJ