You need a pool equipment tech to look at it - could be the motor is buried in leaves or dust or such or has a bad bearing or winding so it is overheating, and a thermal breaker is tripping out, then cutting back in automatically after it cools off. Having the inlet screen/strainear clogged so water is not flowing through it can do this too.
Could also - probably more likely if not a clogged intake or strainer - be an overly sensitive or mis-set pressure trip switch.
Could also be, if your system has one, that the pressure tank has filled with water, so instead of pressuring it up and getting a good period of time with adequate pressure before the pump kicks back on, it is pressuring up the water in the tank (which happens very quickly), so is shutting off at the sthuoff pressure. This results in short-cyhcling of the pump. though not all pool systems have this.
Could also be, depending on how your system is plumbed, something wrong in the clorination or water treaatment unit (if you have an automatic one), or someone messed with a valve that is supposed to be open in normal use.
