Wipers do not work all of the time

It is not a common problem. When they do not work, have you checked to see if there is power to the motor?

Could be the wiper transmission is binding or switch is bad.

During one of these events (wipers not working), disconnect wiper motor connector and check for twelve volts, if twelve volts is read, then binding or a bad motor, if no voltage, then switch.

If you are hearing a whirring noise then there is something stripped or broken at the motor. You will have to remove the motor for inspection. It may be internal plastic gears stripped or the linkage could have come apart inside the cowl area.

First check fuses,
Second check motor ground.
Third check for power at the wiper motor.
If you have power and ground suspect bad motor.