Whether the off-kilter sound you hear in your sump pump is a hum, buzz or a whirring noise, the bottom line is that the device is not working properly if it's making that kind of noise. A humming sump pump is not taking water out of the basement or crawl space and discharging it outside. Do some troubleshooting or call a sump pump technician to avoid problems during the next heavy rain.
If the service area of the sump pump experiences wet conditions and the motor in the sump pump hums but there is no lowering of the water level, an air lock may be to blame. This commonly occurs if the sump dries out often, with exposure of the base. If the sump pump has a vent hole, clear it, then turn the sump pump on and off three or four times via the float switch. If nothing happens or the pump continues humming, it may be clogged.
Humming may result from the incorrect installment of the check valve or the valve sticking in the closed position. A check valve generally includes an arrow, which indicates water flow. Make sure the arrow points upward at "discharge," not "pump."
The humming sound may be the result of a jammed impeller, the mechanical part that draws in water. Generally, debris is clogging the impeller, causing the jam and the resulting noise. After removing the impeller, clean the interior thoroughly. Also make sure none of the impeller's blades are broken. To avoid this problem in the future, install a filter in the sump pump to collect debris.
If the temperature is below freezing and the sump pump hums but doesn't work, suspect a frozen discharge pipe. You may need to use an infrared heater to melt the ice. If the weather is not cold, make sure there are no blockages of other kinds in the pipe. It is possible that the pipe has too many elbows at 90 degrees, which can restrict water flow. Generally, more than three 90-degree elbows means considerable flow reduction. You may have to replace the 90-degree elbows with 45-degree elbows to move water smoothly.