HI,
Thanks for the ideas.
I've already spent a bit of time going through and looking at the resources, seeing what was utilizing the PC at different times, trying to see what it could be, but nothing has stood out.
There is one other strange symptom. When the network does slow down, it seems to take inordinate amounts of CPU to transfer data. If I run a Speedtest I find that my PC comes a little jerky when its showing the maximum 200/200 speed (just after a reboot) but, when the speed has reduced to 50/50 or so) the computer become unresponsive, until the test is done and the results pop up. It's a fairly highly specked PC with a Sandy Lake i5, 16GB ram an a NVME drive.
Unfortunately I don't have time to sit there in safe mode, eliminating one thing at a time to try and find the culprit, but that is probably what I'm going to have to do. I guess I was hoping someone might have an idea :)
Thanks again.
Arran.