I've done a tremendous amount of research into why this might be happening. Emphasis on tremendous.
I tried my best to record a video of the FPS problem and post it on youtube, but the video I recorded over-justifies the problem a bit because the software I've used to create the video lowers my average FPS significantly.
But anyways, I'll show it to you...just pay attention to the extreme FPS drops that occur, most noticeable when the performance overlay literally spikes off the top of the screen and my game freezes for literally seconds on end.
The FPS drops occur on all multiplayer servers regardless of size, map, #players.
The FPS drops occur more frequently when piloting flying vehicles.
The FPS drops occur on a less frequent basis in single player.
I've noticed that when I directly connect my modem to my computer, bypassing the router, it helps slightly but the problem persists. I currently play several other games online without internet connectivity issues.
I will provide any further info necessary to troubleshoot this issue, please just ask.
I just want to play battlefield 3 without dying from FPS spikes. Definitely makes it hard to fly a chopper...