Clogged pump impeller or clogged suction line (been vacuuming leaves?), bad pump-lid "O" ring, loose fitting at front of pump, bad "O" rings in any valves in front of the pump, leak in suction line under ground. These are some of the areas that might cause a problem as you are having. The symptoms are similar but the cause different.

Check for any drain plugs in the hair-and-lint pot that might be loose. If there is a connection between that and the main body of the pump, is there a bad gasket or loose bolts? A drain plug on the main pump body can sometimes result in this, though usually it results in a water leak.

Before you start digging, it might be better to call a leak-detection company so that they can pinpoint the problem.