Help my speakers are farting,,,,

I gotta go with the other guys on this one. I think your girlfriend has a ventriloquist farting talent and is trying to blame it on the speakers. If you didn't have an audio system, she'd probably be trying to blame it on your dog. And if you don't have one, then of course it would be someone or something while the TV was one.
I think you should sell tickets and beer for a session of that and could probably pay for your next pair of speakers with the proceeds. Get her on Dave Letterman!

Is there any odor eminating from around your speakers? Sometimes speakers just impersonate "sneakers" and cut some pretty nasty cheese when you're not looking. I'm sure that you've heard the saying that "these speakers stink"...they actually do!!! Some poor quality sourcing makes them build up back pressure in their chambers and eventually they just got to let er rip.

Ask your girl friend to fart above 200 hz, so you can tell where the sound (or smell) is coming from! :)

(I bet you didn't think you would be getting all of this fun stuff when you wrote your post, did ya!)

As long as you sit downwind you should be fine.

Just as a test for this situation, try pulling your girlfreind's finger with the stereo off! She may be forced to confess her little secret.