Check the water level: Make sure the water level is high enough to cover the skimmer and return jets. If the water level is too low, the filter may be sucking in air, which can cause it to hum.
Clean the filter cartridge: A dirty or clogged filter cartridge can restrict water flow and cause the filter to hum. Remove the filter cartridge and clean it thoroughly with a garden hose.
Inspect the filter housing: Check the filter housing for any cracks or damage that could be causing the humming sound. If you find any damage, replace the filter housing.
Lubricate the filter motor: Over time, the filter motor can become dry and begin to make noise. Turn off the filter and unplug it from the power source. Remove the motor cover and apply a small amount of WD-40 or another lubricant to the motor shaft. Be careful not to over-lubricate, as this could damage the motor.
Check the pump and impeller: If the filter is still humming, the problem may be with the pump or impeller. Disconnect the pump from the power source and remove it from the filter. Check the impeller for any damage and clean it thoroughly with a garden hose. If the impeller is damaged, replace it.
If you have tried all of these steps and the filter is still humming, it is best to contact a professional pool service technician for further assistance.