Ejector pump filling with groundwater?

We bought this house about a year ago, and it has a basement bathroom with an ejector pump, and a separate sump pump. Normally the ejector pump goes off occasionally, normally when it rains. Over the last two weeks it has been going off all the time- sometimes every half hour for no apparant reason. We just had a plumber in who could find no cause for it, but said that he can see a trickle of groundwater coming in constantly. Is there any reason why this would happen all of a sudden? It has not rained here in weeks, and we are in near drought conditions. We do have a storm drain in the back yard, don't know if that is relavent or not. Any thoughts?