It's really strange to be honest, and I can't really explain it. Heres a few things to clear up so you understand the situation.
1) It's not internet lag.
2) It's not server side lag.
3) The games been installed for months without this problem.
4) It is on the latest version.
5) I've tried uninstalling/reinstalling only for it to be fixed till the game restarted.
After I started the game back up, and go onto MP and join a server... It starts up without any problems, when I'm running around in the first few seconds of getting into a server, the game freezes for around 2 seconds every 5 seconds. So it freezes, comes back, then freezes every other 5th second for around 2 seconds each time.
What the hell is going on? I havn't installed/uninstalled anything or updated anything for it to cause this.
Nah, if it were failing hardware like a video card going bad, it would also do that in sp. However, do you play any other online fps's? If so, do they have the same problem? Also make sure the game itself is up-to-date. If other fps's do the same thing, try updating your ethernet drivers, and if that doesn't work, it's either network lag, or hardware failure.