The data are noisy when using libgazebo_ros_ft_sensor.so

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I tried to attach a Force/Torque sensor to the foot of an humanoid robot as follows:

<gazebo>
    <plugin name="left_ft_sensor" filename="libgazebo_ros_ft_sensor.so">
        <updateRate>100.0</updateRate>
        <topicName>/robotis/sensor/left_ft_sensor</topicName>
        <jointName>l_leg_an_r</jointName>
        <gaussianNoise>0.0</gaussianNoise>
    </plugin>
</gazebo>

And the force along z-axis of one foot when the robot was walking is shown as follows:

I tried to add a low-pass filter, but it did not work. Is there any solution to this problem? Thanks in advance.