I’m encountering more instances where I’m timing out on my tests. I think the issue is AdSense. I use it to monetize my site. If you want to see an example, check out http://www.webpagetest.org/result/150307_03_P09/
What I’ve noticed is a huge number of requests that I think belong to ad platforms. I suspect these are some sort of real-time bid systems. Some examples include liverail, altitude-arena, etc.
Ironically, I’ve kept Google over the years as they didn’t put the strain on my site the way other ad networks would. I don’t recall seeing this type of activity before.