Speakers turn electricity into sound -- any electricity. That means that if too much power is going to the speaker or extraneous signals are being picked up by the wiring, it can come through the speakers as static. Stopping static requires finding and eliminating that extra electricity from transmitting through your speakers.
All sorts of technology creates electromagnetic radiation that can, in turn, be picked up by speakers or speaker wire and transmitted as sound. Microwave ovens, mobile phones, Wi-Fi routers, radio and television transmitters and baby monitors all send out EMR that might cause static in speakers. Interference will, in most cases, be intermittent and varied. Get rid of static from interference by using shielded cables, shielded speakers and moving the components away from sources of interference. Speakers designed for computers are shielded while most speakers designed for home audio are not.
Electricity wants to go to ground, and if it does not have a clear path to the ground it may cause shorts and static. Ground loops occur "when two or more devices are connected to a common ground through different paths," according to A/V specialist site Audioholics. If you have a powered amplifier plugged into one grounded outlet and powered speakers plugged into a different grounded outlet, the resulting ground loop can cause hum or buzz in your speakers. Note that the static of a ground loop will be consistent and constant, while static from interference will be variable. You can solve a ground loop by plugging all electrical components into the same grounded circuit. If you have cable television or a mast antenna, the coaxial cable will have its own ground and may be creating a ground loop as well. The use of a isolation transformer for electrical grounds and a cable TV ground isolator for the coaxial cable will solve ground loop problems.
Too Much Power
When the electrical signal that's transmitting the sound to the speakers has too much power it can cause distortion-type static in the sound. If you only notice the static when the volume is turned up, then your static might be a distortion issue. When the speakers, amplifier or microphone can't handle the energy of the sound they just max out and the resulting sound is flattened at the top. If the distortion is on the recording, try switching to a different source. If you're still hearing distortion, turn down the volume on your amplifier until the distortion goes away. If the volume is too low to be easily heard, the problem may be that your amplifier produces too much power for your speakers to handle or that your amp and speakers have different impedance ratings.
If a speaker's cone has been damaged then any sound run through it can cause static by vibrating the damaged bit. A torn or loose cone won't vibrate precisely with the sound of the signal, but will have extra vibrations that cause extra noise. The speaker case or things touching the speaker case can also begin to vibrate when the sound is flowing. Rest your hand gently on different components of the speaker case to see if you can isolate the source of the static. If something is touching the speaker case, move it away. If the case is damaged you may be able to glue or fasten it back together to prevent vibration. If the speaker cone is loose it may be reparable with the proper glue. If the speaker cone is torn or damaged, though, the cone will have to be replaced altogether.