It happens only when i surf internet. I'm using Windows XP version 2002 sp3. Downloading, playing internet games, pinging does not have any kind of lag (or has in the beginning but no spikes when its in process). There is one interesting thing when i change OS to Linux, or if i connect my other computer to this internet connection (one computer at a time) this problem does not happen. So I'm guessing it's software based.
What I've tried:
Uninstalling antivirus program.
Restarting Computer / Modem
Reinstalling drivers / Internet browsers
Nothing seems to have any kind of effect on this issue.
I've never had this kind of problem before so not sure what should i do now. So please help me on this one.