I eventually found the root cause of all my network issues at home and sadly it points to my OMV box. Perhaps someone with a clear understanding of the system could provide some insight to this.
I have a DSL modem router (100mbps) connected to a central 100mbps switch. From there it goes to my study which has a gigabit switch connecting my laptop, desktop, OMV box and 3G WIFI modem router. I started experiencing very bad pings and dropped connections to my DSL router so that browsing the web was bad.
So I found that once I unplug my OMV box from the LAN, my pings to the DSL modem goes to 1ms. Plug it back in again and it all goes erratic.
See pics from ping and ETH interface graphs.
Surely this is not normal?