The toilet keeps flushing on its own - every few minutes. What can I do?

Water pressure makes the unit kick on and off, definitely somehow water is draining back into the pump casing creating enough water pressure that it makes the unit kick on and off by itself. You need to inspect the flapper on the flush valve inside the toilet tank (water closet) make sure is closing all the way down or it may need to be replaced. Also you may want to inspect the check valve inside the discharge elbow, the check valve has a flapper that opens towards the back of the elbow and allows the waste to be pumped out; when the unit stops pumping the flapper closes back down to prevent waste water from draining back into the pump. The check valve may be defective or may be obstructed and closing all the way down as it should. You may just have to clean it, it may be as simple as that.