@johnson - I've probably made the VOIP sound worse than it is. I tend to use the phone for conferencing and have calls of one or two hours in length. When on the calls there will be periods where it goes garbled (usually for the other end of the call i.e. I go garbled), so I sit outside with wifi on the phone turned off. So for me VOIP isn't usable.
The home network has two access points, a Fritzbox upstairs at he east end of the house and an Asus DSL55U downstairs at the west end (that sounds posh - it's just an old long house with solid walls). There are a few Netgear Switches and everything with an ethernet port is wired. Kids had restricted internet access until recently (I did a factory reset on the Fritzbox and haven't put the restrictions back on yet). I don't think they are torrenting, mainly because they don't have anything which won't go to sleep in a few minutes.
It's now much better than it was - the question is, if it normally goes pear shaped at roughly 7pm each evening with a sudden spike of FECs, is that not likely to be REIN (It would likely be present on the QLN as the last reset was overnight). How would I go about finding the source?
Looking at the Ping graph, it mostly behaved last night (I'm not sure I believe the packet loss it's reporting, I mostly see large ping times rather than loss - possibly the timeout is set at 500ms).
I've wandered about with an AM radio on 612Hz and while I can hear noise - I can't correlate it to ping or FEC. I may also have an incorrect assumption that it's one device causing the problem.