DIAGNOSIS A clog in the drain system is blocking the pump. The humming is the pump motor trying, but failing, to turn.
FIX Unplug the machine. Check the drain hose at the back for kinks. Then, access the drain pump filter (usually behind a small kick panel at the front-bottom). Place towels, open the cap slowly, and remove any debris like socks, coins, or lint.
IF THAT DIDN'T WORK The pump impeller might be seized or the pump motor itself might be dead. After clearing any clogs, try to spin the pump impeller by hand through the filter opening. If it doesn't turn freely, the pump needs replacing.
HEADS UP Bail out most of the water from the tub before opening the pump filter, or you'll have a huge spill.