Spikes in your NVPerfHUD profile?

So, I was profiling some stuff today with NVPerfHUD and NVShaderPerf (both tools rock, btw. I really wish ATI would release something like this soon), and I was getting some strange spikes in my profile. These spikes were causing my fps to vary between 3 and 300. Pretty damn annoying.

I wasn't doing anything strange at all, only using 8 meg video memory, and making 12 DP calls per frame. I thought I might be pixel shader limited (I was running 5 passes of a 15-tap Gaussian blur), but changing this to a simple 2 instruction "texture lookup and output" made no difference.



It really did look like some extra work was being done every second. After reading through Nvidias optimizing tricks, and trying to find the culprit, and shut down ICQ by mistake, and lo and behold, the spikes where gone. I started ICQ again, the spikes returned. I suspect some kind of network crap going on every second, but I don't really have any good way of finding out.

And all this before 12 o'clock. Pretty damn freaky.