I've been experiencing large ping spikes and packet loss with Comcast internet over the past year or so. It's been a bigger issue as of late, practically happening every weekend, which can make playing games, or sounding like a robot over Skype, pretty frustrating. I replaced my modem and router, thinking of of them could be the issue, but the problem persists. I contacted Comcast and went through all the basic troubleshooting and none of it worked. I do notice that when they try to ping my modem, they apparently get 10% packet loss.
The odd thing is my internet goes back to being fine the next day, no problems whatsoever. One possible contributor to all this, that I've noticed, is weather. When it's a thunderstorm, bitter cold, or snowing, it seems to happen more than if it were a normal day outside. That doesn't make sense to me though, since I didn't think those things would affect cable internet, but I may be wrong.
I've also found a bunch of other threads in various forums about the same issue in the Chicago area, and Comcast obviously just ignores it. I just want to get to the bottom line of what's causing this and get what I'm paying for, which is to not have broken internet for a day, practically once a week.