Because the spikes start at hop 1, you know the problem starts at hop 1, or maybe earlier (like in your computer). The first hop that shows problems is where you have to attribute the problem - not anything downstream. All traffic has to go through hop 1, so if the problem shows up at hop 1 you can't blame hop 2.

We have a wireless access point here that used to do something similar, and somewhere along the way (probably a bios update), it just stopped having the problem. Try removing components in your system to see if you can isolate the problem - if you're using a wireless router, try wiring it. If you have another computer, try that and see if you get the same results.

- Pete