How often should my sump pump come on?

I just bought a house and I've noticed that my sump pump comes on about every 30-45 minutes. Thats seems a bit excessive so I'm wondering if it needs to be replaced. The house is about 4 years old and it sits at the bottom of a hill so I'm told the sump pump comes on because I get the water from the homes that sit above me. I would appreciate any advise or ideas as I am a first time home owner. Thanks. i also forgot to mention. The house was not winterized before we bought it so the sprinkler system busted. But we turned off the water to the sprinkler...so that should stop water from flowing to the sprinklers, right? Besides, its winter and we wont be using the sprinklers until Spring so we werent concerned about fixing it right away...unless it is what's causing the sump pump to kick on..hmmmm :)