Sounds like an interesting problem to diagnose. Have you tried having the TV remote by your side and when you hear the interference in your speakers, immediately turn off - or on - the TV to see whether that affects things? Since radio waves can travel a fair distance, it could be something as simple as a neighbor with a new gizmo that isn't radio shielded or emits way more static than it should.

There are also some other possible culprits, not the least of which can be a GSM-based phone. The most common? An iPhone. You can test this: put an iPhone very close to a radio or powered speaker system and sometimes you'll hear a cyclic interference pattern. My understanding is that it's just part of the way the phone checks in with the local cell tower.

Microsoft is also aware of static interference issues with its mouse and has a tech note with the scintillating title of Troubleshoot response failures in wireless keyboard or mouse that offers up some possible solutions to your problem...

I should note that these debugging tips are for wireless, not bluetooth-based mice and keyboards. Bluetooth is a whole 'nother beast...

First method to try is to resync your mouse with the receiver. This is done by pressing the button on the receiver unit until it starts blinking, then using a pen or pin or similar to push the tiny sync button on the bottom of the mouse, as highlighted below:

The second possibility to try and fix the problem is to simply use a different USB port on your computer. Just unplug the receiver unit and plug it into a different port on your computer, then make sure it's sync'd. If your mouse is hooked up via a PS/2 plug, however, note that it's recommended you power down your computer, switch plugs, then turn it on again. Yeah, that's why we're fans of the hot-plugged USB port. :-)

Third possibility should probably be the first: try a fresh set of batteries. Sometimes, apparently, when the batteries are getting low the device becomes more susceptible to interference. New batteries = less problem.

Finally, Microsoft also has a rather amusing note about things around your computer that could be causing interference:

"Items such as wireless routers, radios, cell phones, desktop fans, fluorescent lights, and large metal objects like computer cases and metal furniture may interfere with the signal of the keyboard. Try to keep such items away from the keyboard, and check the behavior of the keyboard.

"Do not put the mouse or the receiver near any electrical devices, especially transmitters such as cordless or cellular telephones or other wireless mouse devices or receivers. A distance of at least 8 to 12 inches is recommended. Do not put the mouse or the receiver on metallic surfaces or objects, especially long metallic rails or cables. We recommend that you keep the mouse and the keyboard a minimum of 3 feet from metallic objects."

Anyway, between all of these, I hope something will help you out. Go test, experiment and let us know what helped you out!