CS problem

Whenever i play counter strike in steam offline mode, i get sudden mouse sensitivity spikes for a split second which is a real annoyance when im recording or just playing some maps. It even happens sometimes when im in steam online mode i.e when im listening to music on itunes. I know my computer is capable of handling CS super smoothly with lots of programs loaded. But this strange issue persists. Anyone with ideas? it would be great if someone could help.