I'm glad i found this thread. I'm fairly new to 3D printing and have a lot to learn. That's why I'm here. My story... I bought a Printrbot Metal Simple about 2 months ago. I have printed about 300 hours so far. I love this little printer. I noticed the "ringing" or "echoing" in my parts somewhere after about 125-150 hours were on the machine. I also noticed it's sound changed a bit. It picked up a slight vibration noise that i can not pinpoint. and it seems to be getting worse. I think its in the y axis stepper motor. Most of my "echoing waves" appear on the x axis face durring printing so that might make sense if the y-axis motor is having an issue (i.e. the y-axis is ping-ponging back and fourth following a y axis move while the x is traversing in a strait line) this printing a wave effect on the X axis face of the part. I'm guessing the motor is going bad. How many hours are stepper motors typically good for before the tend to wear out or "go bad in some way" Printrbot used some pretty chunky NEMA 17 steppers that physically appear to be very well built. I can't imagine it would wear out that fast. I'll try to post some pics tonight of the parts with the echoing before 100 hours and after 150 hours to show the difference. This is why I'm not to sure this issue is software / acceleration related. I think i might order a fresh set of GT2 belts and do a little maintenance and tighten some screws next week to see if it clears up the issue.