Hi, I own both arduino and a sonar (ultrasonic sensor). I do robotics research and have tons of experience with sensors and data filtering. I will need for you to deffine what will you consider as noise for your measurments. Note that the sensor itself has internal noise, and if this is the type of noise you want to filter it can be done only with other inputs and methods such as Kalman Filter. But if the noise you are refering to is filtering out small objects or very short readings of the sensor, then this can be done with arduino code. Please msg me with any questions you might have.
Regards,
Ivan