I experience this exact type of lag spikes all the time, it starts giving me lag spikes every two seconds or so for about 20-30 seconds and then it runs perfect and smooth for about 3 minutes then starts all over again. It happens to me on every map at the begining and then every 3min or so after that, I traced the problem to Punkbuster B and disabled it, I then loaded into a map and it was perfect and smooth for the first time since punkbusterB came out, then punkbuster kicked me for not running PunkbusterB.
Next time it happens, alt-tab out of game and look at your processes in task manager, I'm just curious if this happens to anyone else, I am in the process of getting rid of punkbuster B completely, makes the game completely un-playable while this is happening and I have to find a quiet spot to wait and sit it out.
Very frustrating