We also saw occational spikes when trying to use this sensor, I don't recall exactly how we had it set up when we were testing but it would spike to full distance. We went back to the datasheet for the maxbotix and noticed
our sensor has a 20 Hz reading rate. We changed are loop rate to 20 Hz and never saw spikes again.
Our competition bot uses the PWM signal from the Maxbotix sensor and is used to detect the ball.