What idle behaviors can disrupt a network connection?

Question

I've got a PC with a wireless card installed. I've been having fits of bad performance, but I've narrowed down one of the many things I'd like to fix.

It seems if my computer idles for some period of time I haven't measured, something goes haywire and I my network adapter starts toggling its state. If I babysit the machine and keep it busy I go through good and bad bandwidth periods, but if it's left alone I get cycling periods with no activity. This is a picture of an experiment I ran to confirm. I added a red line to indicate where the screensaver came on, and a blue line indicates where I wiggled the mouse after 30 seconds or so.

To rule out the screensaver itself, I turned off the screensaver and sat down to play some Metroid. When I looked up after a while, I saw this (the spike is where I poked the mouse to see if it would make a change; it happened almost instantaneously:)

So it's not the screensaver. But I can't figure out what it is. My system is set to never automatically sleep. In device manager the network adapter had an option to let Windows turn it off to save power; I unchecked this option. The only setting left is I've allowed Windows to turn off hard drives after 20 minutes; shouldn't that notice disk activity and leave my disk alone? Besides, while typing this I had to help my wife with some stuff and in 5 minutes this behavior had started. If I sit at the computer and constantly move the mouse, I see no degredation in performance. I'd rather be able to leave my computer unattended.

Any ideas what could cause this?

*update*

I've got a preliminary answer. I'm using the CrashPlan backup service, and it seems like it's sort of jealous of the files it's got an eye on. I had suspected this earlier and dropped any download folders I could find from the backup, but I found one I had missed. Dropping that folder from the backup seems to have made a big difference. I'll queue up some more downloads and see if that helps.

Answer 1

I'm not going to accept this answer because it's me, but here is the solution in case someone else has similar issues.

It looks like the major factor was CrashPlan. If you're running a backup service, it might see the downloading files as something that needs to be backed up. This can lock the file and make it inaccessible. I seem to remember Mozy didn't have this issue but I'm not going back to them. I solved it by secluding my downloads in a special folder and excluding that folder from my backup.

It looks like Avast! virus scan was also contributing to sluggish performance. On a lark, I temporarily disabled it and while download speed didn't change the download application got much more responsive and reliable. Microsoft Security Essentials doesn't seem to be getting in the way like Avast! did.