Hmmm . . . I don't really think it's either the X-Fi, nor the speakers themself . . . going to need some more in-depth info, there; Are you're speakers connected through minijacks, RCA or S/PDIF? When does it typically occur, when the PC is on or off, when the subwoofer is on or off? It's possible voltage spikes through the line might cause the woofer to kick, but, if it happens at somewhat regular intervals, it might be power electrical interference - a central HVAC unit can cause this, as well as most modern appliances. If you leave anywhere near a public utilites lot of some sort, that too could cause problems. TBH, I'd recommend a good, high-end surge protector any how, as that will help control most of it - if it's still present, a power conditioner might be in order, also. Also, as I'm not sure the exact capabilities of that speaker setup; do they have some kind of energy saving feature, where they go into a 'standby' mode if not being used for a while? If so, it's quite possible the kick you're hearing is from the sub turning on and then back off. But, I must ask also, are there any high powered wireless phones near the unit? A WiFi network router? Do you charge your cell phone near by the subwoofer, especially with it being on? If so, you might want to remove these items from the room, and see if the woofer is still randomly kicking.