Ping lag/stutter multiple times a minute

Specs:
i5, 8GB Ram, R9 290, Win8.1

While playing TTT, I get a stutter every 10-20 seconds making it difficult to play.
Using the net graph, you can see the ping spike (lowest red bars)eg.

I have another machine and this problem does not occur there(same network)

I tried;
validating files, steam said 2 failed and downloaded them
moving from a HDD to a SDD
quitting the wireless adapter software
checked Windows Firewall
switching server
switching gamemode
disabling addons

Any ideas of what could be causing the problem would be greatly appreciated

(I will probably re download GMod tonight)

Is your other machine using wireless as well?

Try using a network cable instead?

Yes the other machine is using wireless
My router is downstairs so I cant connect a network cable, sorry