I have a near-mint 97 740i with 62k miles. About 6 months ago I noticed that there is what sounds like a short burst of static from the speakers from time to time. It only lasts a half a second and does not come at any regular interval. I've tried to watch and listen to see if the noise appears at the same time as some other function the car is performing, but no luck. Whether moving or at a stop, it happens unpredictabily.
The wierd thing is that the stereo does not even need to be powered on - which leads me to believe that it is some sort of static discharge.