Anti-lock Brake Servo Noise?

[pishta]

Dads 91 SC400 135k. I hear a cyclic noise coming from the ABS control unit, or whatever the ABS thing is to the left of the radiator, sounds like power steering pump. comes and goes usually for about 4-5 seconds at a time minutes or hours apart. while stopped or driveing. Was told not to worry about it by the old ownerr, but any random noise sparks my interest in an otherwise silent car. Car is showroom maintained. thanks

[djspawn00]

My gs3 was doing the same thing, apparently its normal.