I keep hearing bursts of static from the speakers of my electronic keyboard. At first I thought there was a loose electrical connection, but sometimes it has a rhythmic pattern to it, like “rat tatatat tatatat tatatat.” And once I think I heard it coming from my computer speakers too. What is causing these strange noises?
The noises are caused by electronics picking up wireless signals from your mobile phone and translating the interference into sound. Well-shielded circuits won't have this problem, but it's common in consumer electronics and some musical equipment, notably guitar leads. There's no damage to your equipment, and if the sound is a problem just keep the phone away from your electronic components and signal cables.
The above two answers are correct, however, here is some more details:
It's called electrostatic interference. It's caused by unbalanced cables picking up radio waves, basically acting as a radio antenna. If you are using an amplifier or a loud speaker this may be fixed by running a balanced cable instead or an unbalanced cable. If you go to purchase one this is what you want to look for: